# WASI Core API This is the API-level documentation for WASI Core. The function names are prefixed with "\_\_wasi\_" to reflect how they are spelled in flat-namespace contexts, however at the wasm module level, they are unprefixed, because they're inside a module namespace (currently "wasi\_unstable"). Functions that start with `__wasi_fd_` operate on file descriptors, while functions that start with `__wasi_path_` operate on filesystem paths, which are relative to directory file descriptors. Much inspiration and content here is derived from [CloudABI] and [POSIX], though there are also several differences from CloudABI and POSIX. For example, WASI Core has no concept of processes in the traditional Unix sense. While wasm linear memories have some of the aspects of processes, and it's possible to *emulate* the full semantics of processes on top of them, this can sometimes be unnatural and inefficient. The goal for WASI Core is to be a WebAssembly-native API that exposes APIs that fit well into the underlying WebAssembly platform, rather than to directly emulate other platforms. This is also a work in progress, and the API here is still evolving. [CloudABI]: https://github.com/NuxiNL/cloudabi [POSIX]: http://pubs.opengroup.org/onlinepubs/9699919799/ ## System calls - [`__wasi_args_get()`](#args_get) - [`__wasi_args_sizes_get()`](#args_sizes_get) - [`__wasi_clock_res_get()`](#clock_res_get) - [`__wasi_clock_time_get()`](#clock_time_get) - [`__wasi_environ_get()`](#environ_get) - [`__wasi_environ_sizes_get()`](#environ_sizes_get) - [`__wasi_fd_advise()`](#fd_advise) - [`__wasi_fd_allocate()`](#fd_allocate) - [`__wasi_fd_close()`](#fd_close) - [`__wasi_fd_datasync()`](#fd_datasync) - [`__wasi_fd_fdstat_get()`](#fd_fdstat_get) - [`__wasi_fd_fdstat_set_flags()`](#fd_fdstat_set_flags) - [`__wasi_fd_fdstat_set_rights()`](#fd_fdstat_set_rights) - [`__wasi_fd_filestat_get()`](#fd_filestat_get) - [`__wasi_fd_filestat_set_size()`](#fd_filestat_set_size) - [`__wasi_fd_filestat_set_times()`](#fd_filestat_set_times) - [`__wasi_fd_pread()`](#fd_pread) - [`__wasi_fd_prestat_dir_name()`](#fd_prestat_dir_name) - [`__wasi_fd_prestat_get()`](#fd_prestat_get) - [`__wasi_fd_pwrite()`](#fd_pwrite) - [`__wasi_fd_read()`](#fd_read) - [`__wasi_fd_readdir()`](#fd_readdir) - [`__wasi_fd_renumber()`](#fd_renumber) - [`__wasi_fd_seek()`](#fd_seek) - [`__wasi_fd_sync()`](#fd_sync) - [`__wasi_fd_tell()`](#fd_tell) - [`__wasi_fd_write()`](#fd_write) - [`__wasi_path_create_directory()`](#path_create_directory) - [`__wasi_path_filestat_get()`](#path_filestat_get) - [`__wasi_path_filestat_set_times()`](#path_filestat_set_times) - [`__wasi_path_link()`](#path_link) - [`__wasi_path_open()`](#path_open) - [`__wasi_path_readlink()`](#path_readlink) - [`__wasi_path_remove_directory()`](#path_remove_directory) - [`__wasi_path_rename()`](#path_rename) - [`__wasi_path_symlink()`](#path_symlink) - [`__wasi_path_unlink_file()`](#path_unlink_file) - [`__wasi_poll_oneoff()`](#poll_oneoff) - [`__wasi_proc_exit()`](#proc_exit) - [`__wasi_proc_raise()`](#proc_raise) - [`__wasi_random_get()`](#random_get) - [`__wasi_sched_yield()`](#sched_yield) - [`__wasi_sock_recv()`](#sock_recv) - [`__wasi_sock_send()`](#sock_send) - [`__wasi_sock_shutdown()`](#sock_shutdown) ### `__wasi_args_get()` Read command-line argument data. The sizes of the buffers should match that returned by [`__wasi_args_sizes_get()`](#args_sizes_get). Inputs: - char \*\*argv A pointer to a buffer to write the argument pointers. - char \*argv\_buf A pointer to a buffer to write the argument string data. ### `__wasi_args_sizes_get()` Return command-line argument data sizes. Outputs: - size\_t argc The number of arguments. - size\_t argv\_buf\_size The size of the argument string data. ### `__wasi_clock_res_get()` Return the resolution of a clock. Implementations are required to provide a non-zero value for supported clocks. For unsupported clocks, return [`__WASI_EINVAL`](#errno.inval). Note: This is similar to `clock_getres` in POSIX. Inputs: - [\_\_wasi\_clockid\_t](#clockid) clock\_id The clock for which to return the resolution. Outputs: - [\_\_wasi\_timestamp\_t](#timestamp) resolution The resolution of the clock. ### `__wasi_clock_time_get()` Return the time value of a clock. Note: This is similar to `clock_gettime` in POSIX. Inputs: - [\_\_wasi\_clockid\_t](#clockid) clock\_id The clock for which to return the time. - [\_\_wasi\_timestamp\_t](#timestamp) precision The maximum lag (exclusive) that the returned time value may have, compared to its actual value. Outputs: - [\_\_wasi\_timestamp\_t](#timestamp) time The time value of the clock. ### `__wasi_environ_get()` Read environment variable data. The sizes of the buffers should match that returned by [`__wasi_environ_sizes_get()`](#environ_sizes_get). Inputs: - char \*\*environ A pointer to a buffer to write the environment variable pointers. - char \*environ\_buf A pointer to a buffer to write the environment variable string data. ### `__wasi_environ_sizes_get()` Return environment variable data sizes. Outputs: - size\_t environ\_count The number of environment variables. - size\_t environ\_buf\_size The size of the environment variable string data. ### `__wasi_fd_advise()` Provide file advisory information on a file descriptor. Note: This is similar to `posix_fadvise` in POSIX. Inputs: - [\_\_wasi\_fd\_t](#fd) fd The file descriptor for the file for which to provide file advisory information. - [\_\_wasi\_filesize\_t](#filesize) offset The offset within the file to which the advisory applies. - [\_\_wasi\_filesize\_t](#filesize) len The length of the region to which the advisory applies. - [\_\_wasi\_advice\_t](#advice) advice The advice. ### `__wasi_fd_allocate()` Force the allocation of space in a file. Note: This is similar to `posix_fallocate` in POSIX. Inputs: - [\_\_wasi\_fd\_t](#fd) fd The file descriptor for the file in which to allocate space. - [\_\_wasi\_filesize\_t](#filesize) offset The offset at which to start the allocation. - [\_\_wasi\_filesize\_t](#filesize) len The length of the area that is allocated. ### `__wasi_fd_close()` Close a file descriptor. Note: This is similar to `close` in POSIX. Inputs: - [\_\_wasi\_fd\_t](#fd) fd The file descriptor to close. ### `__wasi_fd_datasync()` Synchronize the data of a file to disk. Note: This is similar to `fdatasync` in POSIX. Inputs: - [\_\_wasi\_fd\_t](#fd) fd The file descriptor of the file to synchronize to disk. ### `__wasi_fd_fdstat_get()` Get the attributes of a file descriptor. Note: This returns similar flags to `fcntl(fd, F_GETFL)` in POSIX, as well as additional fields. Inputs: - [\_\_wasi\_fd\_t](#fd) fd The file descriptor to inspect. - [\_\_wasi\_fdstat\_t](#fdstat) \*buf The buffer where the file descriptor's attributes are stored. ### `__wasi_fd_fdstat_set_flags()` Adjust the flags associated with a file descriptor. Note: This is similar to `fcntl(fd, F_SETFL, flags)` in POSIX. Inputs: - [\_\_wasi\_fd\_t](#fd) fd The file descriptor to operate on. - [\_\_wasi\_fdflags\_t](#fdflags) flags The desired values of the file descriptor flags. ### `__wasi_fd_fdstat_set_rights()` Adjust the rights associated with a file descriptor. This can only be used to remove rights, and returns [`__WASI_ENOTCAPABLE`](#errno.notcapable) if called in a way that would attempt to add rights. Inputs: - [\_\_wasi\_fd\_t](#fd) fd The file descriptor to operate on. - [\_\_wasi\_rights\_t](#rights) fs\_rights\_base The desired base rights of the file descriptor. - [\_\_wasi\_rights\_t](#rights) fs\_rights\_inheriting The desired inheriting rights of the file descriptor. ### `__wasi_fd_filestat_get()` Return the attributes of an open file. Inputs: - [\_\_wasi\_fd\_t](#fd) fd The file descriptor to inspect. - [\_\_wasi\_filestat\_t](#filestat) \*buf The buffer where the file's attributes are stored. ### `__wasi_fd_filestat_set_size()` Adjust the size of an open file. If this increases the file's size, the extra bytes are filled with zeros. Note: This is similar to `ftruncate` in POSIX. Inputs: - [\_\_wasi\_fd\_t](#fd) fd A file descriptor for the file to adjust. - [\_\_wasi\_filesize\_t](#filesize) st\_size The desired file size. ### `__wasi_fd_filestat_set_times()` Adjust the timestamps of an open file or directory. Note: This is similar to `futimens` in POSIX. Inputs: - [\_\_wasi\_fd\_t](#fd) fd The file descriptor to operate on. - [\_\_wasi\_timestamp\_t](#timestamp) st\_atim The desired values of the data access timestamp. - [\_\_wasi\_timestamp\_t](#timestamp) st\_mtim The desired values of the data modification timestamp. - [\_\_wasi\_fstflags\_t](#fstflags) fst\_flags A bitmask indicating which timestamps to adjust. ### `__wasi_fd_pread()` Read from a file descriptor, without using and updating the file descriptor's offset. Note: This is similar to `preadv` in POSIX. Inputs: - [\_\_wasi\_fd\_t](#fd) fd The file descriptor from which to read data. - const [\_\_wasi\_iovec\_t](#iovec) \*iovs and size\_t iovs\_len List of scatter/gather vectors in which to store data. - [\_\_wasi\_filesize\_t](#filesize) offset The offset within the file at which to read. Outputs: - size\_t nread The number of bytes read. ### `__wasi_fd_prestat_dir_name()` Return a description of the given preopened file descriptor. Inputs: - [\_\_wasi\_fd\_t](#fd) fd The file descriptor about which to retrieve information. - const char \*path and size\_t path\_len A buffer into which to write the preopened directory name. ### `__wasi_fd_prestat_get()` Return a description of the given preopened file descriptor. Inputs: - [\_\_wasi\_fd\_t](#fd) fd The file descriptor about which to retrieve information. - [\_\_wasi\_prestat\_t](#prestat) \*buf The buffer where the description is stored. ### `__wasi_fd_pwrite()` Write to a file descriptor, without using and updating the file descriptor's offset. Note: This is similar to `pwritev` in POSIX. Inputs: - [\_\_wasi\_fd\_t](#fd) fd The file descriptor to which to write data. - const [\_\_wasi\_ciovec\_t](#ciovec) \*iovs and size\_t iovs\_len List of scatter/gather vectors from which to retrieve data. - [\_\_wasi\_filesize\_t](#filesize) offset The offset within the file at which to write. Outputs: - size\_t nwritten The number of bytes written. ### `__wasi_fd_read()` Read from a file descriptor. Note: This is similar to `readv` in POSIX. Inputs: - [\_\_wasi\_fd\_t](#fd) fd The file descriptor from which to read data. - const [\_\_wasi\_iovec\_t](#iovec) \*iovs and size\_t iovs\_len List of scatter/gather vectors to which to store data. Outputs: - size\_t nread The number of bytes read. ### `__wasi_fd_readdir()` Read directory entries from a directory. When successful, the contents of the output buffer consist of a sequence of directory entries. Each directory entry consists of a [`__wasi_dirent_t`](#dirent) object, followed by [`__wasi_dirent_t::d_namlen`](#dirent.d_namlen) bytes holding the name of the directory entry. This function fills the output buffer as much as possible, potentially truncating the last directory entry. This allows the caller to grow its read buffer size in case it's too small to fit a single large directory entry, or skip the oversized directory entry. Inputs: - [\_\_wasi\_fd\_t](#fd) fd The directory from which to read the directory entries. - void \*buf and size\_t buf\_len The buffer where directory entries are stored. - [\_\_wasi\_dircookie\_t](#dircookie) cookie The location within the directory to start reading. Outputs: - size\_t bufused The number of bytes stored in the read buffer. If less than the size of the read buffer, the end of the directory has been reached. ### `__wasi_fd_renumber()` Atomically replace a file descriptor by renumbering another file descriptor. Due to the strong focus on thread safety, this environment does not provide a mechanism to duplicate or renumber a file descriptor to an arbitrary number, like dup2(). This would be prone to race conditions, as an actual file descriptor with the same number could be allocated by a different thread at the same time. This function provides a way to atomically renumber file descriptors, which would disappear if dup2() were to be removed entirely. Inputs: - [\_\_wasi\_fd\_t](#fd) from The file descriptor to renumber. - [\_\_wasi\_fd\_t](#fd) to The file descriptor to overwrite. ### `__wasi_fd_seek()` Move the offset of a file descriptor. Note: This is similar to `lseek` in POSIX. Inputs: - [\_\_wasi\_fd\_t](#fd) fd The file descriptor to operate on. - [\_\_wasi\_filedelta\_t](#filedelta) offset The number of bytes to move. - [\_\_wasi\_whence\_t](#whence) whence The base from which the offset is relative. Outputs: - [\_\_wasi\_filesize\_t](#filesize) newoffset The new offset of the file descriptor, relative to the start of the file. ### `__wasi_fd_sync()` Synchronize the data and metadata of a file to disk. Note: This is similar to `fsync` in POSIX. Inputs: - [\_\_wasi\_fd\_t](#fd) fd The file descriptor of the file containing the data and metadata to synchronize to disk. ### `__wasi_fd_tell()` Return the current offset of a file descriptor. Note: This is similar to `lseek(fd, 0, SEEK_CUR)` in POSIX. Inputs: - [\_\_wasi\_fd\_t](#fd) fd The file descriptor to inspect. Outputs: - [\_\_wasi\_filesize\_t](#filesize) offset The current offset of the file descriptor, relative to the start of the file. ### `__wasi_fd_write()` Write to a file descriptor. Note: This is similar to `writev` in POSIX. Inputs: - [\_\_wasi\_fd\_t](#fd) fd The file descriptor to which to write data. - const [\_\_wasi\_ciovec\_t](#ciovec) \*iovs and size\_t iovs\_len List of scatter/gather vectors from which to retrieve data. Outputs: - size\_t nwritten The number of bytes written. ### `__wasi_path_create_directory()` Create a directory. Note: This is similar to `mkdirat` in POSIX. Inputs: - [\_\_wasi\_fd\_t](#fd) fd The working directory at which the resolution of the path starts. - const char \*path and size\_t path\_len The path at which to create the directory. ### `__wasi_path_filestat_get()` Return the attributes of a file or directory. Note: This is similar to `stat` in POSIX. Inputs: - [\_\_wasi\_fd\_t](#fd) fd The working directory at which the resolution of the path starts. - [\_\_wasi\_lookupflags\_t](#lookupflags) flags Flags determining the method of how the path is resolved. - const char \*path and size\_t path\_len The path of the file or directory to inspect. - [\_\_wasi\_filestat\_t](#filestat) \*buf The buffer where the file's attributes are stored. ### `__wasi_path_filestat_set_times()` Adjust the timestamps of a file or directory. Note: This is similar to `utimensat` in POSIX. Inputs: - [\_\_wasi\_fd\_t](#fd) fd The working directory at which the resolution of the path starts. - [\_\_wasi\_lookupflags\_t](#lookupflags) flags Flags determining the method of how the path is resolved. - const char \*path and size\_t path\_len The path of the file or directory to operate on. - [\_\_wasi\_timestamp\_t](#timestamp) st\_atim The desired values of the data access timestamp. - [\_\_wasi\_timestamp\_t](#timestamp) st\_mtim The desired values of the data modification timestamp. - [\_\_wasi\_fstflags\_t](#fstflags) fst\_flags A bitmask indicating which timestamps to adjust. ### `__wasi_path_link()` Create a hard link. Note: This is similar to `linkat` in POSIX. Inputs: - [\_\_wasi\_fd\_t](#fd) old\_fd The working directory at which the resolution of the old path starts. - [\_\_wasi\_lookupflags\_t](#lookupflags) old\_flags Flags determining the method of how the path is resolved. - const char \*old\_path and size\_t old\_path\_len The source path from which to link. - [\_\_wasi\_fd\_t](#fd) new\_fd The working directory at which the resolution of the new path starts. - const char \*new\_path and size\_t new\_path\_len The destination path at which to create the hard link. ### `__wasi_path_open()` Open a file or directory. The returned file descriptor is not guaranteed to be the lowest-numbered file descriptor not currently open; it is randomized to prevent applications from depending on making assumptions about indexes, since this is error-prone in multi-threaded contexts. The returned file descriptor is guaranteed to be less than 2³¹. Note: This is similar to `openat` in POSIX. Inputs: - [\_\_wasi\_fd\_t](#fd) dirfd The working directory at which the resolution of the path starts. - [\_\_wasi\_lookupflags\_t](#lookupflags) dirflags Flags determining the method of how the path is resolved. - const char \*path and size\_t path\_len The path of the file or directory to open. - [\_\_wasi\_oflags\_t](#oflags) o_flags The method by which to open the file. - [\_\_wasi\_rights\_t](#rights) fs\_rights\_base The initial base rights of the newly created file descriptor. The implementation is allowed to return a file descriptor with fewer rights than specified, if and only if those rights do not apply to the type of file being opened. The *base* rights are rights that will apply to operations using the file descriptor itself. - [\_\_wasi\_rights\_t](#rights) fs\_rights\_inheriting The initial inheriting rights of the newly created file descriptor. The implementation is allowed to return a file descriptor with fewer rights than specified, if and only if those rights do not apply to the type of file being opened. The *inheriting* rights are rights that will apply to file descriptors derived from the file descriptor itself. - [\_\_wasi\_fdflags\_t](#fdflags) fs\_flags The initial flags of the file descriptor. Outputs: - [\_\_wasi\_fd\_t](#fd) fd The file descriptor of the file that has been opened. ### `__wasi_path_readlink()` Read the contents of a symbolic link. Note: This is similar to `readlinkat` in POSIX. Inputs: - [\_\_wasi\_fd\_t](#fd) fd The working directory at which the resolution of the path starts. - const char \*path and size\_t path\_len The path of the symbolic link from which to read. - char \*buf and size\_t buf\_len The buffer to which to write the contents of the symbolic link. Outputs: - size\_t bufused The number of bytes placed in the buffer. ### `__wasi_path_remove_directory()` Remove a directory. Return [`__WASI_ENOTEMPTY`](#errno.notempty) if the directory is not empty. Note: This is similar to `unlinkat(fd, path, AT_REMOVEDIR)` in POSIX. Inputs: - [\_\_wasi\_fd\_t](#fd) fd The working directory at which the resolution of the path starts. - const char \*path and size\_t path\_len The path to a directory to remove. ### `__wasi_path_rename()` Rename a file or directory. Note: This is similar to `renameat` in POSIX. Inputs: - [\_\_wasi\_fd\_t](#fd) old\_fd The working directory at which the resolution of the old path starts. - const char \*old\_path and size\_t old\_path\_len The source path of the file or directory to rename. - [\_\_wasi\_fd\_t](#fd) new\_fd The working directory at which the resolution of the new path starts. - const char \*new\_path and size\_t new\_path\_len The destination path to which to rename the file or directory. ### `__wasi_path_symlink()` Create a symbolic link. Note: This is similar to `symlinkat` in POSIX. Inputs: - const char \*old\_path and size\_t old_path\_len The contents of the symbolic link. - [\_\_wasi\_fd\_t](#fd) fd The working directory at which the resolution of the path starts. - const char \*new\_path and size\_t new\_path\_len The destination path at which to create the symbolic link. ### `__wasi_path_unlink_file()` Unlink a file. Return [`__WASI_EISDIR`](#errno.isdir) if the path refers to a directory. Note: This is similar to `unlinkat(fd, path, 0)` in POSIX. Inputs: - [\_\_wasi\_fd\_t](#fd) fd The working directory at which the resolution of the path starts. - const char \*path and size\_t path\_len The path to a file to unlink. ### `__wasi_poll_oneoff()` Concurrently poll for the occurrence of a set of events. Inputs: - const [\_\_wasi\_subscription\_t](#subscription) \*in The events to which to subscribe. - [\_\_wasi\_event\_t](#event) \*out The events that have occurred. - size\_t nsubscriptions Both the number of subscriptions and events. Outputs: - size\_t nevents The number of events stored. ### `__wasi_proc_exit()` Terminate the process normally. An exit code of 0 indicates successful termination of the program. The meanings of other values is dependent on the environment. Note: This is similar to `_Exit` in POSIX. Inputs: - [\_\_wasi\_exitcode\_t](#exitcode) rval The exit code returned by the process. Does not return. ### `__wasi_proc_raise()` Send a signal to the process of the calling thread. Note: This is similar to `raise` in POSIX. Inputs: - [\_\_wasi\_signal\_t](#signal) sig The signal condition to trigger. ### `__wasi_random_get()` Write high-quality random data into a buffer. This function blocks when the implementation is unable to immediately provide sufficient high-quality random data. This function may execute slowly, so when large mounts of random data are required, it's advisable to use this function to seed a pseudo-random number generator, rather than to provide the random data directly. Inputs: - void \*buf and size\_t buf\_len The buffer to fill with random data. ### `__wasi_sched_yield()` Temporarily yield execution of the calling thread. Note: This is similar to `sched_yield` in POSIX. ### `__wasi_sock_recv()` Receive a message from a socket. Note: This is similar to `recv` in POSIX, though it also supports reading the data into multiple buffers in the manner of `readv`. Inputs: - [\_\_wasi\_fd\_t](#fd) sock The socket on which to receive data. - const [\_\_wasi\_iovec\_t](#iovec) \*ri\_data and size\_t ri\_data\_len List of scatter/gather vectors to which to store data. - [\_\_wasi\_riflags\_t](#riflags) ri\_flags Message flags. Outputs: - size\_t ro\_datalen Number of bytes stored in [`ri_data`](#sock_recv.ri_data). - [\_\_wasi\_roflags\_t](#roflags) ro\_flags Message flags. ### `__wasi_sock_send()` Send a message on a socket. Note: This is similar to `send` in POSIX, though it also supports writing the data from multiple buffers in the manner of `writev`. Inputs: - [\_\_wasi\_fd\_t](#fd) sock The socket on which to send data. - const [\_\_wasi\_ciovec\_t](#ciovec) \*si\_data and size\_t si\_data\_len List of scatter/gather vectors to which to retrieve data. - [\_\_wasi\_siflags\_t](#siflags) si\_flags Message flags. Outputs: - size\_t so\_datalen Number of bytes transmitted. ### `__wasi_sock_shutdown()` Shut down socket send and receive channels. Note: This is similar to `shutdown` in POSIX. Inputs: - [\_\_wasi\_fd\_t](#fd) sock The socket on which to shutdown channels. - [\_\_wasi\_sdflags\_t](#sdflags) how Which channels on the socket to shut down. ## Types ### `__wasi_advice_t` (`uint8_t`) File or memory access pattern advisory information. Used by [`__wasi_fd_advise()`](#fd_advise). Possible values: - **`__WASI_ADVICE_DONTNEED`** The application expects that it will not access the specified data in the near future. - **`__WASI_ADVICE_NOREUSE`** The application expects to access the specified data once and then not reuse it thereafter. - **`__WASI_ADVICE_NORMAL`** The application has no advice to give on its behavior with respect to the specified data. - **`__WASI_ADVICE_RANDOM`** The application expects to access the specified data in a random order. - **`__WASI_ADVICE_SEQUENTIAL`** The application expects to access the specified data sequentially from lower offsets to higher offsets. - **`__WASI_ADVICE_WILLNEED`** The application expects to access the specified data in the near future. ### `__wasi_ciovec_t` (`struct`) A region of memory for scatter/gather writes. Used by [`__wasi_fd_pwrite()`](#fd_pwrite), [`__wasi_fd_write()`](#fd_write), and [`__wasi_sock_send()`](#sock_send). Members: - const void \*buf and size\_t buf\_len The address and length of the buffer to be written. ### `__wasi_clockid_t` (`uint32_t`) Identifiers for clocks. Used by [`__wasi_subscription_t`](#subscription), [`__wasi_clock_res_get()`](#clock_res_get), and [`__wasi_clock_time_get()`](#clock_time_get). Possible values: - **`__WASI_CLOCK_MONOTONIC`** The store-wide monotonic clock, which is defined as a clock measuring real time, whose value cannot be adjusted and which cannot have negative clock jumps. The epoch of this clock is undefined. The absolute time value of this clock therefore has no meaning. - **`__WASI_CLOCK_PROCESS_CPUTIME_ID`** The CPU-time clock associated with the current process. - **`__WASI_CLOCK_REALTIME`** The clock measuring real time. Time value zero corresponds with 1970-01-01T00:00:00Z. - **`__WASI_CLOCK_THREAD_CPUTIME_ID`** The CPU-time clock associated with the current thread. ### `__wasi_device_t` (`uint64_t`) Identifier for a device containing a file system. Can be used in combination with [`__wasi_inode_t`](#inode) to uniquely identify a file or directory in the filesystem. Used by [`__wasi_filestat_t`](#filestat). ### `__wasi_dircookie_t` (`uint64_t`) A reference to the offset of a directory entry. Used by [`__wasi_dirent_t`](#dirent) and [`__wasi_fd_readdir()`](#fd_readdir). Special values: - **`__WASI_DIRCOOKIE_START`** Permanent reference to the first directory entry within a directory. ### `__wasi_dirent_t` (`struct`) A directory entry. Members: - [\_\_wasi\_dircookie\_t](#dircookie) d\_next The offset of the next directory entry stored in this directory. - [\_\_wasi\_inode\_t](#inode) d\_ino The serial number of the file referred to by this directory entry. - uint32\_t d\_namlen The length of the name of the directory entry. - [\_\_wasi\_filetype\_t](#filetype) d\_type The type of the file referred to by this directory entry. ### `__wasi_errno_t` (`uint16_t`) Error codes returned by functions. Not all of these error codes are returned by the functions provided by this API; some are used in higher-level library layers, and others are provided merely for alignment with POSIX. Used by [`__wasi_event_t`](#event). Possible values: - **`__WASI_ESUCCESS`** No error occurred. System call completed successfully. - **`__WASI_E2BIG`** Argument list too long. - **`__WASI_EACCES`** Permission denied. - **`__WASI_EADDRINUSE`** Address in use. - **`__WASI_EADDRNOTAVAIL`** Address not available. - **`__WASI_EAFNOSUPPORT`** Address family not supported. - **`__WASI_EAGAIN`** Resource unavailable, or operation would block. - **`__WASI_EALREADY`** Connection already in progress. - **`__WASI_EBADF`** Bad file descriptor. - **`__WASI_EBADMSG`** Bad message. - **`__WASI_EBUSY`** Device or resource busy. - **`__WASI_ECANCELED`** Operation canceled. - **`__WASI_ECHILD`** No child processes. - **`__WASI_ECONNABORTED`** Connection aborted. - **`__WASI_ECONNREFUSED`** Connection refused. - **`__WASI_ECONNRESET`** Connection reset. - **`__WASI_EDEADLK`** Resource deadlock would occur. - **`__WASI_EDESTADDRREQ`** Destination address required. - **`__WASI_EDOM`** Mathematics argument out of domain of function. - **`__WASI_EDQUOT`** Reserved. - **`__WASI_EEXIST`** File exists. - **`__WASI_EFAULT`** Bad address. - **`__WASI_EFBIG`** File too large. - **`__WASI_EHOSTUNREACH`** Host is unreachable. - **`__WASI_EIDRM`** Identifier removed. - **`__WASI_EILSEQ`** Illegal byte sequence. - **`__WASI_EINPROGRESS`** Operation in progress. - **`__WASI_EINTR`** Interrupted function. - **`__WASI_EINVAL`** Invalid argument. - **`__WASI_EIO`** I/O error. - **`__WASI_EISCONN`** Socket is connected. - **`__WASI_EISDIR`** Is a directory. - **`__WASI_ELOOP`** Too many levels of symbolic links. - **`__WASI_EMFILE`** File descriptor value too large. - **`__WASI_EMLINK`** Too many links. - **`__WASI_EMSGSIZE`** Message too large. - **`__WASI_EMULTIHOP`** Reserved. - **`__WASI_ENAMETOOLONG`** Filename too long. - **`__WASI_ENETDOWN`** Network is down. - **`__WASI_ENETRESET`** Connection aborted by network. - **`__WASI_ENETUNREACH`** Network unreachable. - **`__WASI_ENFILE`** Too many files open in system. - **`__WASI_ENOBUFS`** No buffer space available. - **`__WASI_ENODEV`** No such device. - **`__WASI_ENOENT`** No such file or directory. - **`__WASI_ENOEXEC`** Executable file format error. - **`__WASI_ENOLCK`** No locks available. - **`__WASI_ENOLINK`** Reserved. - **`__WASI_ENOMEM`** Not enough space. - **`__WASI_ENOMSG`** No message of the desired type. - **`__WASI_ENOPROTOOPT`** Protocol not available. - **`__WASI_ENOSPC`** No space left on device. - **`__WASI_ENOSYS`** Function not supported. - **`__WASI_ENOTCONN`** The socket is not connected. - **`__WASI_ENOTDIR`** Not a directory or a symbolic link to a directory. - **`__WASI_ENOTEMPTY`** Directory not empty. - **`__WASI_ENOTRECOVERABLE`** State not recoverable. - **`__WASI_ENOTSOCK`** Not a socket. - **`__WASI_ENOTSUP`** Not supported, or operation not supported on socket. - **`__WASI_ENOTTY`** Inappropriate I/O control operation. - **`__WASI_ENXIO`** No such device or address. - **`__WASI_EOVERFLOW`** Value too large to be stored in data type. - **`__WASI_EOWNERDEAD`** Previous owner died. - **`__WASI_EPERM`** Operation not permitted. - **`__WASI_EPIPE`** Broken pipe. - **`__WASI_EPROTO`** Protocol error. - **`__WASI_EPROTONOSUPPORT`** Protocol not supported. - **`__WASI_EPROTOTYPE`** Protocol wrong type for socket. - **`__WASI_ERANGE`** Result too large. - **`__WASI_EROFS`** Read-only file system. - **`__WASI_ESPIPE`** Invalid seek. - **`__WASI_ESRCH`** No such process. - **`__WASI_ESTALE`** Reserved. - **`__WASI_ETIMEDOUT`** Connection timed out. - **`__WASI_ETXTBSY`** Text file busy. - **`__WASI_EXDEV`** Cross-device link. - **`__WASI_ENOTCAPABLE`** Extension: Capabilities insufficient. ### `__wasi_event_t` (`struct`) An event that occurred. Used by [`__wasi_poll_oneoff()`](#poll_oneoff). Members: - [\_\_wasi\_userdata\_t](#userdata) userdata User-provided value that got attached to [`__wasi_subscription_t::userdata`](#subscription.userdata). - [\_\_wasi\_errno\_t](#errno) error If non-zero, an error that occurred while processing the subscription request. - [\_\_wasi\_eventtype\_t](#eventtype) type The type of the event that occurred. - When `type` is [`__WASI_EVENTTYPE_FD_READ`](#eventtype.fd_read) or [`__WASI_EVENTTYPE_FD_WRITE`](#eventtype.fd_write): - **`u.fd_readwrite`** - [\_\_wasi\_filesize\_t](#filesize) nbytes The number of bytes available for reading or writing. - [\_\_wasi\_eventrwflags\_t](#eventrwflags) flags The state of the file descriptor. ### `__wasi_eventrwflags_t` (`uint16_t` bitfield) The state of the file descriptor subscribed to with [`__WASI_EVENTTYPE_FD_READ`](#eventtype.fd_read) or [`__WASI_EVENTTYPE_FD_WRITE`](#eventtype.fd_write). Used by [`__wasi_event_t`](#event). Possible values: - **`__WASI_EVENT_FD_READWRITE_HANGUP`** The peer of this socket has closed or disconnected. ### `__wasi_eventtype_t` (`uint8_t`) Type of a subscription to an event or its occurrence. Used by [`__wasi_event_t`](#event) and [`__wasi_subscription_t`](#subscription). Possible values: - **`__WASI_EVENTTYPE_CLOCK`** The time value of clock [`__wasi_subscription_t::u.clock.clock_id`](#subscription.u.clock.clock_id) has reached timestamp [`__wasi_subscription_t::u.clock.timeout`](#subscription.u.clock.timeout). - **`__WASI_EVENTTYPE_FD_READ`** File descriptor [`__wasi_subscription_t::u.fd_readwrite.fd`](#subscription.u.fd_readwrite.fd) has data available for reading. This event always triggers for regular files. - **`__WASI_EVENTTYPE_FD_WRITE`** File descriptor [`__wasi_subscription_t::u.fd_readwrite.fd`](#subscription.u.fd_readwrite.fd) has capacity available for writing. This event always triggers for regular files. ### `__wasi_exitcode_t` (`uint32_t`) Exit code generated by a process when exiting. Used by [`__wasi_proc_exit()`](#proc_exit). ### `__wasi_fd_t` (`uint32_t`) A file descriptor number. Used by many functions in this API. As in POSIX, three file descriptor numbers are provided to instances on startup -- 0, 1, and 2, (a.k.a. `STDIN_FILENO`, `STDOUT_FILENO`, and `STDERR_FILENO`). Starting at 3 follow a possibly-entry sequence of preopened file descriptors provided by the host environment; information about these may be obtained through [`__wasi_fd_prestat_get()`](#fd_prestat_get). Other than these, WASI implementations are not required to allocate new file descriptors in ascending order. ### `__wasi_fdflags_t` (`uint16_t` bitfield) File descriptor flags. Used by [`__wasi_fdstat_t`](#fdstat), [`__wasi_fd_fdstat_set_flags()`](#fd_fdstat_set_flags), and [`__wasi_path_open()`](#path_open). Possible values: - **`__WASI_FDFLAG_APPEND`** Append mode: Data written to the file is always appended to the file's end. - **`__WASI_FDFLAG_DSYNC`** Write according to synchronized I/O data integrity completion. Only the data stored in the file is synchronized. - **`__WASI_FDFLAG_NONBLOCK`** Non-blocking mode. - **`__WASI_FDFLAG_RSYNC`** Synchronized read I/O operations. - **`__WASI_FDFLAG_SYNC`** Write according to synchronized I/O file integrity completion. In addition to synchronizing the data stored in the file, the implementation may also synchronously update the file's metadata. ### `__wasi_fdstat_t` (`struct`) File descriptor attributes. Used by [`__wasi_fd_fdstat_get()`](#fd_fdstat_get). Members: - [\_\_wasi\_filetype\_t](#filetype) fs\_filetype File type. - [\_\_wasi\_fdflags\_t](#fdflags) fs\_flags File descriptor flags. - [\_\_wasi\_rights\_t](#rights) fs\_rights\_base Rights that apply to this file descriptor. - [\_\_wasi\_rights\_t](#rights) fs\_rights\_inheriting Maximum set of rights that may be installed on new file descriptors that are created through this file descriptor, e.g., through [`__wasi_path_open()`](#path_open). ### `__wasi_filedelta_t` (`int64_t`) Relative offset within a file. Used by [`__wasi_fd_seek()`](#fd_seek). ### `__wasi_filesize_t` (`uint64_t`) Non-negative file size or length of a region within a file. Used by [`__wasi_event_t`](#event), [`__wasi_filestat_t`](#filestat), [`__wasi_fd_advise()`](#fd_advise), [`__wasi_fd_allocate()`](#fd_allocate), [`__wasi_fd_filestat_set_size()`](#fd_filestat_set_size), [`__wasi_fd_pread()`](#fd_pread), [`__wasi_fd_pwrite()`](#fd_pwrite), [`__wasi_fd_seek()`](#fd_seek), and [`__wasi_fd_tell()`](#fd_tell). ### `__wasi_filestat_t` (`struct`) File attributes. Used by [`__wasi_fd_filestat_get()`](#fd_filestat_get) and [`__wasi_path_filestat_get()`](#path_filestat_get). Members: - [\_\_wasi\_device\_t](#device) st\_dev Device ID of device containing the file. - [\_\_wasi\_inode\_t](#inode) st\_ino File serial number. - [\_\_wasi\_filetype\_t](#filetype) st\_filetype File type. - [\_\_wasi\_linkcount\_t](#linkcount) st\_nlink Number of hard links to the file. - [\_\_wasi\_filesize\_t](#filesize) st\_size For regular files, the file size in bytes. For symbolic links, the length in bytes of the pathname contained in the symbolic link. - [\_\_wasi\_timestamp\_t](#timestamp) st\_atim Last data access timestamp. - [\_\_wasi\_timestamp\_t](#timestamp) st\_mtim Last data modification timestamp. - [\_\_wasi\_timestamp\_t](#timestamp) st\_ctim Last file status change timestamp. ### `__wasi_filetype_t` (`uint8_t`) The type of a file descriptor or file. Used by [`__wasi_dirent_t`](#dirent), [`__wasi_fdstat_t`](#fdstat), and [`__wasi_filestat_t`](#filestat). Possible values: - **`__WASI_FILETYPE_UNKNOWN`** The type of the file descriptor or file is unknown or is different from any of the other types specified. - **`__WASI_FILETYPE_BLOCK_DEVICE`** The file descriptor or file refers to a block device inode. - **`__WASI_FILETYPE_CHARACTER_DEVICE`** The file descriptor or file refers to a character device inode. - **`__WASI_FILETYPE_DIRECTORY`** The file descriptor or file refers to a directory inode. - **`__WASI_FILETYPE_REGULAR_FILE`** The file descriptor or file refers to a regular file inode. - **`__WASI_FILETYPE_SOCKET_DGRAM`** The file descriptor or file refers to a datagram socket. - **`__WASI_FILETYPE_SOCKET_STREAM`** The file descriptor or file refers to a byte-stream socket. - **`__WASI_FILETYPE_SYMBOLIC_LINK`** The file refers to a symbolic link inode. ### `__wasi_fstflags_t` (`uint16_t` bitfield) Which file time attributes to adjust. Used by [`__wasi_fd_filestat_set_times()`](#fd_filestat_set_times) and [`__wasi_path_filestat_set_times()`](#path_filestat_set_times). Possible values: - **`__WASI_FILESTAT_SET_ATIM`** Adjust the last data access timestamp to the value stored in [`__wasi_filestat_t::st_atim`](#filestat.st_atim). - **`__WASI_FILESTAT_SET_ATIM_NOW`** Adjust the last data access timestamp to the time of clock [`__WASI_CLOCK_REALTIME`](#clockid.realtime). - **`__WASI_FILESTAT_SET_MTIM`** Adjust the last data modification timestamp to the value stored in [`__wasi_filestat_t::st_mtim`](#filestat.st_mtim). - **`__WASI_FILESTAT_SET_MTIM_NOW`** Adjust the last data modification timestamp to the time of clock [`__WASI_CLOCK_REALTIME`](#clockid.realtime). ### `__wasi_inode_t` (`uint64_t`) File serial number that is unique within its file system. Used by [`__wasi_dirent_t`](#dirent) and [`__wasi_filestat_t`](#filestat). ### `__wasi_iovec_t` (`struct`) A region of memory for scatter/gather reads. Used by [`__wasi_fd_pread()`](#fd_pread), [`__wasi_fd_read()`](#fd_read), and [`__wasi_sock_recv()`](#sock_recv). Members: - void \*buf and size\_t buf\_len The address and length of the buffer to be filled. ### `__wasi_linkcount_t` (`uint32_t`) Number of hard links to an inode. Used by [`__wasi_filestat_t`](#filestat). ### `__wasi_lookupflags_t` (`uint32_t` bitfield) Flags determining the method of how paths are resolved. Used by [`__wasi_path_filestat_get()`](#path_filestat_get), [`__wasi_path_filestat_set_times()`](#path_filestat_set_times), [`__wasi_path_link()`](#path_link), and [`__wasi_path_open()`](#path_open). Possible values: - **`__WASI_LOOKUP_SYMLINK_FOLLOW`** As long as the resolved path corresponds to a symbolic link, it is expanded. ### `__wasi_oflags_t` (`uint16_t` bitfield) Open flags used by [`__wasi_path_open()`](#path_open). Used by [`__wasi_path_open()`](#path_open). Possible values: - **`__WASI_O_CREAT`** Create file if it does not exist. - **`__WASI_O_DIRECTORY`** Fail if not a directory. - **`__WASI_O_EXCL`** Fail if file already exists. - **`__WASI_O_TRUNC`** Truncate file to size 0. ### `__wasi_preopentype_t` (`uint8_t`) Preopened resource type. Used by [`__wasi_prestat_t`](#prestat). Possible values: - **`__WASI_PREOPENTYPE_DIR`** Preopened directory. ### `__wasi_prestat_t` (`struct`) Information about a preopened resource. Used by [`__wasi_fd_prestat_get()`](#fd_prestat_get). Members: - [\_\_wasi\_preopentype\_t](#preopentype) pr\_type The type of the preopened resource. - When `pr_type` is [`__WASI_PREOPENTYPE_DIR`](#preopentype.dir): - size\_t u.pr\_name\_len The length of the preopened directory name. ### `__wasi_riflags_t` (`uint16_t` bitfield) Flags provided to [`__wasi_sock_recv()`](#sock_recv). Used by [`__wasi_sock_recv()`](#sock_recv). Possible values: - **`__WASI_SOCK_RECV_PEEK`** Returns the message without removing it from the socket's receive queue. - **`__WASI_SOCK_RECV_WAITALL`** On byte-stream sockets, block until the full amount of data can be returned. ### `__wasi_rights_t` (`uint64_t` bitfield) File descriptor rights, determining which actions may be performed. Used by [`__wasi_fdstat_t`](#fdstat), [`__wasi_fd_fdstat_set_rights()`](#fd_fdstat_set_rights), and [`__wasi_path_open()`](#path_open). Possible values: - **`__WASI_RIGHT_FD_DATASYNC`** The right to invoke [`__wasi_fd_datasync()`](#fd_datasync). If [`__WASI_RIGHT_PATH_OPEN`](#rights.path_open) is set, includes the right to invoke [`__wasi_path_open()`](#path_open) with [`__WASI_FDFLAG_DSYNC`](#fdflags.dsync). - **`__WASI_RIGHT_FD_READ`** The right to invoke [`__wasi_fd_read()`](#fd_read) and [`__wasi_sock_recv()`](#sock_recv). If [`__WASI_RIGHT_FD_SEEK`](#rights.fd_seek) is set, includes the right to invoke [`__wasi_fd_pread()`](#fd_pread). - **`__WASI_RIGHT_FD_SEEK`** The right to invoke [`__wasi_fd_seek()`](#fd_seek). This flag implies [`__WASI_RIGHT_FD_TELL`](#rights.fd_tell). - **`__WASI_RIGHT_FD_FDSTAT_SET_FLAGS`** The right to invoke [`__wasi_fd_fdstat_set_flags()`](#fd_fdstat_set_flags). - **`__WASI_RIGHT_FD_SYNC`** The right to invoke [`__wasi_fd_sync()`](#fd_sync). If [`__WASI_RIGHT_PATH_OPEN`](#rights.path_open) is set, includes the right to invoke [`__wasi_path_open()`](#path_open) with [`__WASI_FDFLAG_RSYNC`](#fdflags.rsync) and [`__WASI_FDFLAG_DSYNC`](#fdflags.dsync). - **`__WASI_RIGHT_FD_TELL`** The right to invoke [`__wasi_fd_seek()`](#fd_seek) in such a way that the file offset remains unaltered (i.e., [`__WASI_WHENCE_CUR`](#whence.cur) with offset zero), or to invoke [`__wasi_fd_tell()`](#fd_tell). - **`__WASI_RIGHT_FD_WRITE`** The right to invoke [`__wasi_fd_write()`](#fd_write) and [`__wasi_sock_send()`](#sock_send). If [`__WASI_RIGHT_FD_SEEK`](#rights.fd_seek) is set, includes the right to invoke [`__wasi_fd_pwrite()`](#fd_pwrite). - **`__WASI_RIGHT_FD_ADVISE`** The right to invoke [`__wasi_fd_advise()`](#fd_advise). - **`__WASI_RIGHT_FD_ALLOCATE`** The right to invoke [`__wasi_fd_allocate()`](#fd_allocate). - **`__WASI_RIGHT_PATH_CREATE_DIRECTORY`** The right to invoke [`__wasi_path_create_directory()`](#path_create_directory). - **`__WASI_RIGHT_PATH_CREATE_FILE`** If [`__WASI_RIGHT_PATH_OPEN`](#rights.path_open) is set, the right to invoke [`__wasi_path_open()`](#path_open) with [`__WASI_O_CREAT`](#oflags.creat). - **`__WASI_RIGHT_PATH_LINK_SOURCE`** The right to invoke [`__wasi_path_link()`](#path_link) with the file descriptor as the source directory. - **`__WASI_RIGHT_PATH_LINK_TARGET`** The right to invoke [`__wasi_path_link()`](#path_link) with the file descriptor as the target directory. - **`__WASI_RIGHT_PATH_OPEN`** The right to invoke [`__wasi_path_open()`](#path_open). - **`__WASI_RIGHT_FD_READDIR`** The right to invoke [`__wasi_fd_readdir()`](#fd_readdir). - **`__WASI_RIGHT_PATH_READLINK`** The right to invoke [`__wasi_path_readlink()`](#path_readlink). - **`__WASI_RIGHT_PATH_RENAME_SOURCE`** The right to invoke [`__wasi_path_rename()`](#path_rename) with the file descriptor as the source directory. - **`__WASI_RIGHT_PATH_RENAME_TARGET`** The right to invoke [`__wasi_path_rename()`](#path_rename) with the file descriptor as the target directory. - **`__WASI_RIGHT_PATH_FILESTAT_GET`** The right to invoke [`__wasi_path_filestat_get()`](#path_filestat_get). - **`__WASI_RIGHT_PATH_FILESTAT_SET_SIZE`** The right to change a file's size (there is no `__wasi_path_filestat_set_size()`). If [`__WASI_RIGHT_PATH_OPEN`](#rights.path_open) is set, includes the right to invoke [`__wasi_path_open()`](#path_open) with [`__WASI_O_TRUNC`](#oflags.trunc). - **`__WASI_RIGHT_PATH_FILESTAT_SET_TIMES`** The right to invoke [`__wasi_path_filestat_set_times()`](#path_filestat_set_times). - **`__WASI_RIGHT_FD_FILESTAT_GET`** The right to invoke [`__wasi_fd_filestat_get()`](#fd_filestat_get). - **`__WASI_RIGHT_FD_FILESTAT_SET_SIZE`** The right to invoke [`__wasi_fd_filestat_set_size()`](#fd_filestat_set_size). - **`__WASI_RIGHT_FD_FILESTAT_SET_TIMES`** The right to invoke [`__wasi_fd_filestat_set_times()`](#fd_filestat_set_times). - **`__WASI_RIGHT_PATH_SYMLINK`** The right to invoke [`__wasi_path_symlink()`](#path_symlink). - **`__WASI_RIGHT_PATH_UNLINK_FILE`** The right to invoke [`__wasi_path_unlink_file()`](#path_unlink_file). - **`__WASI_RIGHT_PATH_REMOVE_DIRECTORY`** The right to invoke [`__wasi_path_remove_directory()`](#path_remove_directory). - **`__WASI_RIGHT_POLL_FD_READWRITE`** If [`__WASI_RIGHT_FD_READ`](#rights.fd_read) is set, includes the right to invoke [`__wasi_poll_oneoff()`](#poll_oneoff) to subscribe to [`__WASI_EVENTTYPE_FD_READ`](#eventtype.fd_read). If [`__WASI_RIGHT_FD_WRITE`](#rights.fd_write) is set, includes the right to invoke [`__wasi_poll_oneoff()`](#poll_oneoff) to subscribe to [`__WASI_EVENTTYPE_FD_WRITE`](#eventtype.fd_write). - **`__WASI_RIGHT_SOCK_SHUTDOWN`** The right to invoke [`__wasi_sock_shutdown()`](#sock_shutdown). ### `__wasi_roflags_t` (`uint16_t` bitfield) Flags returned by [`__wasi_sock_recv()`](#sock_recv). Used by [`__wasi_sock_recv()`](#sock_recv). Possible values: - **`__WASI_SOCK_RECV_DATA_TRUNCATED`** Returned by [`__wasi_sock_recv()`](#sock_recv): Message data has been truncated. ### `__wasi_sdflags_t` (`uint8_t` bitfield) Which channels on a socket to shut down. Used by [`__wasi_sock_shutdown()`](#sock_shutdown). Possible values: - **`__WASI_SHUT_RD`** Disables further receive operations. - **`__WASI_SHUT_WR`** Disables further send operations. ### `__wasi_siflags_t` (`uint16_t` bitfield) Flags provided to [`__wasi_sock_send()`](#sock_send). As there are currently no flags defined, it must be set to zero. Used by [`__wasi_sock_send()`](#sock_send). ### `__wasi_signal_t` (`uint8_t`) Signal condition. Used by [`__wasi_proc_raise()`](#proc_raise). Possible values: - **`__WASI_SIGABRT`** Process abort signal. Action: Terminates the process. - **`__WASI_SIGALRM`** Alarm clock. Action: Terminates the process. - **`__WASI_SIGBUS`** Access to an undefined portion of a memory object. Action: Terminates the process. - **`__WASI_SIGCHLD`** Child process terminated, stopped, or continued. Action: Ignored. - **`__WASI_SIGCONT`** Continue executing, if stopped. Action: Continues executing, if stopped. - **`__WASI_SIGFPE`** Erroneous arithmetic operation. Action: Terminates the process. - **`__WASI_SIGHUP`** Hangup. Action: Terminates the process. - **`__WASI_SIGILL`** Illegal instruction. Action: Terminates the process. - **`__WASI_SIGINT`** Terminate interrupt signal. Action: Terminates the process. - **`__WASI_SIGKILL`** Kill. Action: Terminates the process. - **`__WASI_SIGPIPE`** Write on a pipe with no one to read it. Action: Ignored. - **`__WASI_SIGQUIT`** Terminal quit signal. Action: Terminates the process. - **`__WASI_SIGSEGV`** Invalid memory reference. Action: Terminates the process. - **`__WASI_SIGSTOP`** Stop executing. Action: Stops executing. - **`__WASI_SIGSYS`** Bad system call. Action: Terminates the process. - **`__WASI_SIGTERM`** Termination signal. Action: Terminates the process. - **`__WASI_SIGTRAP`** Trace/breakpoint trap. Action: Terminates the process. - **`__WASI_SIGTSTP`** Terminal stop signal. Action: Stops executing. - **`__WASI_SIGTTIN`** Background process attempting read. Action: Stops executing. - **`__WASI_SIGTTOU`** Background process attempting write. Action: Stops executing. - **`__WASI_SIGURG`** High bandwidth data is available at a socket. Action: Ignored. - **`__WASI_SIGUSR1`** User-defined signal 1. Action: Terminates the process. - **`__WASI_SIGUSR2`** User-defined signal 2. Action: Terminates the process. - **`__WASI_SIGVTALRM`** Virtual timer expired. Action: Terminates the process. - **`__WASI_SIGXCPU`** CPU time limit exceeded. Action: Terminates the process. - **`__WASI_SIGXFSZ`** File size limit exceeded. Action: Terminates the process. ### `__wasi_subclockflags_t` (`uint16_t` bitfield) Flags determining how to interpret the timestamp provided in [`__wasi_subscription_t::u.clock.timeout`](#subscription.u.clock.timeout). Used by [`__wasi_subscription_t`](#subscription). Possible values: - **`__WASI_SUBSCRIPTION_CLOCK_ABSTIME`** If set, treat the timestamp provided in [`__wasi_subscription_t::u.clock.timeout`](#subscription.u.clock.timeout) as an absolute timestamp of clock [`__wasi_subscription_t::u.clock.clock_id`](#subscription.u.clock.clock_id). If clear, treat the timestamp provided in [`__wasi_subscription_t::u.clock.timeout`](#subscription.u.clock.timeout) relative to the current time value of clock [`__wasi_subscription_t::u.clock.clock_id`](#subscription.u.clock.clock_id). ### `__wasi_subscription_t` (`struct`) Subscription to an event. Used by [`__wasi_poll_oneoff()`](#poll_oneoff). Members: - [\_\_wasi\_userdata\_t](#userdata) userdata User-provided value that is attached to the subscription in the implementation and returned through [`__wasi_event_t::userdata`](#event.userdata). - [\_\_wasi\_eventtype\_t](#eventtype) type The type of the event to which to subscribe. - When `type` is [`__WASI_EVENTTYPE_CLOCK`](#eventtype.u.clock): - **`u.clock`** - [\_\_wasi\_userdata\_t](#userdata) identifier The user-defined unique identifier of the clock. - [\_\_wasi\_clockid\_t](#clockid) clock\_id The clock against which to compare the timestamp. - [\_\_wasi\_timestamp\_t](#timestamp) timeout The absolute or relative timestamp. - [\_\_wasi\_timestamp\_t](#timestamp) precision The amount of time that the implementation may wait additionally to coalesce with other events. - [\_\_wasi\_subclockflags\_t](#subclockflags) flags Flags specifying whether the timeout is absolute or relative. - When `type` is [`__WASI_EVENTTYPE_FD_READ`](#eventtype.fd_read) or [`__WASI_EVENTTYPE_FD_WRITE`](#eventtype.fd_write): - **`u.fd_readwrite`** - [\_\_wasi\_fd\_t](#fd) fd The file descriptor on which to wait for it to become ready for reading or writing. ### `__wasi_timestamp_t` (`uint64_t`) Timestamp in nanoseconds. Used by [`__wasi_filestat_t`](#filestat), [`__wasi_subscription_t`](#subscription), [`__wasi_clock_res_get()`](#clock_res_get), [`__wasi_clock_time_get()`](#clock_time_get), [`__wasi_fd_filestat_set_times()`](#fd_filestat_set_times), and [`__wasi_path_filestat_set_times()`](#path_filestat_set_times). ### `__wasi_userdata_t` (`uint64_t`) User-provided value that may be attached to objects that is retained when extracted from the implementation. Used by [`__wasi_event_t`](#event) and [`__wasi_subscription_t`](#subscription). ### `__wasi_whence_t` (`uint8_t`) The position relative to which to set the offset of the file descriptor. Used by [`__wasi_fd_seek()`](#fd_seek). Possible values: - **`__WASI_WHENCE_CUR`** Seek relative to current position. - **`__WASI_WHENCE_END`** Seek relative to end-of-file. - **`__WASI_WHENCE_SET`** Seek relative to start-of-file.