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wasmtime/docs/WASI-api.md
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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.

System calls

__wasi_args_get()

Read command-line argument data.

The sizes of the buffers should match that returned by __wasi_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.

Note: This is similar to clock_getres in POSIX.

Inputs:

Outputs:

__wasi_clock_time_get()

Return the time value of a clock.

Note: This is similar to clock_gettime in POSIX.

Inputs:

  • __wasi_clockid_t clock_id

    The clock for which to return the time.

  • __wasi_timestamp_t precision

    The maximum lag (exclusive) that the returned time value may have, compared to its actual value.

Outputs:

__wasi_environ_get()

Read environment variable data.

The sizes of the buffers should match that returned by __wasi_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_allocate()

Force the allocation of space in a file.

Note: This is similar to posix_fallocate in POSIX.

Inputs:

__wasi_fd_close()

Close a file descriptor.

Note: This is similar to close in POSIX.

Inputs:

__wasi_fd_datasync()

Synchronize the data of a file to disk.

Note: This is similar to fdatasync in POSIX.

Inputs:

  • __wasi_fd_t 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

    The file descriptor to inspect.

  • __wasi_fdstat_t *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_fdstat_set_rights()

Adjust the rights associated with a file descriptor.

This can only be used to remove rights, and returns __WASI_ENOTCAPABLE if called in a way that would attempt to add rights.

Inputs:

  • __wasi_fd_t fd

    The file descriptor to operate on.

  • __wasi_rights_t fs_rights_base

    The desired base rights of the file descriptor.

  • __wasi_rights_t 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_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_filestat_set_times()

Adjust the timestamps of an open file or directory.

Note: This is similar to futimens in POSIX.

Inputs:

__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

    The file descriptor from which to read data.

  • const __wasi_iovec_t *iovs and size_t iovs_len

    List of scatter/gather vectors in which to store data.

  • __wasi_filesize_t 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

    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

    The file descriptor about which to retrieve information.

  • __wasi_prestat_t *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

    The file descriptor to which to write data.

  • const __wasi_ciovec_t *iovs and size_t iovs_len

    List of scatter/gather vectors from which to retrieve data.

  • __wasi_filesize_t 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

    The file descriptor from which to read data.

  • const __wasi_iovec_t *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 object, followed by __wasi_dirent_t::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

    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 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_seek()

Move the offset of a file descriptor.

Note: This is similar to lseek in POSIX.

Inputs:

Outputs:

  • __wasi_filesize_t 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

    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:

Outputs:

  • __wasi_filesize_t 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

    The file descriptor to which to write data.

  • const __wasi_ciovec_t *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

    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

    The working directory at which the resolution of the path starts.

  • __wasi_lookupflags_t 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 *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

    The working directory at which the resolution of the path starts.

  • __wasi_lookupflags_t 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 st_atim

    The desired values of the data access timestamp.

  • __wasi_timestamp_t st_mtim

    The desired values of the data modification timestamp.

  • __wasi_fstflags_t 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 old_fd

    The working directory at which the resolution of the old path starts.

  • __wasi_lookupflags_t 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 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 dirfd

    The working directory at which the resolution of the path starts.

  • __wasi_lookupflags_t dirflags

    Flags determining the method of how the path is resolved.

  • const char *path and size_t path_len

    The relative path of the file or directory to open, relative to the dirfd directory.

  • __wasi_oflags_t o_flags

    The method by which to open the file.

  • __wasi_rights_t 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 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 fs_flags

    The initial flags of the file descriptor.

Outputs:

  • __wasi_fd_t 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

    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 if the directory is not empty.

Note: This is similar to unlinkat(fd, path, AT_REMOVEDIR) in POSIX.

Inputs:

  • __wasi_fd_t 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 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 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

    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 if the path refers to a directory.

Note: This is similar to unlinkat(fd, path, 0) in POSIX.

Inputs:

  • __wasi_fd_t 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 *in

    The events to which to subscribe.

  • __wasi_event_t *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:

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_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:

Outputs:

__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:

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:

Types

__wasi_advice_t (uint8_t)

File or memory access pattern advisory information.

Used by __wasi_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(), __wasi_fd_write(), and __wasi_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, __wasi_clock_res_get(), and __wasi_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 to uniquely identify a file or directory in the filesystem.

Used by __wasi_filestat_t.

__wasi_dircookie_t (uint64_t)

A reference to the offset of a directory entry.

Used by __wasi_dirent_t and __wasi_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 d_next

    The offset of the next directory entry stored in this directory.

  • __wasi_inode_t 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 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.

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().

Members:

__wasi_eventrwflags_t (uint16_t bitfield)

The state of the file descriptor subscribed to with __WASI_EVENTTYPE_FD_READ or __WASI_EVENTTYPE_FD_WRITE.

Used by __wasi_event_t.

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 and __wasi_subscription_t.

Possible values:

__wasi_exitcode_t (uint32_t)

Exit code generated by a process when exiting.

Used by __wasi_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().

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, __wasi_fd_fdstat_set_flags(), and __wasi_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().

Members:

__wasi_filedelta_t (int64_t)

Relative offset within a file.

Used by __wasi_fd_seek().

__wasi_filesize_t (uint64_t)

Non-negative file size or length of a region within a file.

Used by __wasi_event_t, __wasi_filestat_t, __wasi_fd_advise(), __wasi_fd_allocate(), __wasi_fd_filestat_set_size(), __wasi_fd_pread(), __wasi_fd_pwrite(), __wasi_fd_seek(), and __wasi_fd_tell().

__wasi_filestat_t (struct)

File attributes.

Used by __wasi_fd_filestat_get() and __wasi_path_filestat_get().

Members:

__wasi_filetype_t (uint8_t)

The type of a file descriptor or file.

Used by __wasi_dirent_t, __wasi_fdstat_t, and __wasi_filestat_t.

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() and __wasi_path_filestat_set_times().

Possible values:

__wasi_inode_t (uint64_t)

File serial number that is unique within its file system.

Used by __wasi_dirent_t and __wasi_filestat_t.

__wasi_iovec_t (struct)

A region of memory for scatter/gather reads.

Used by __wasi_fd_pread(), __wasi_fd_read(), and __wasi_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.

__wasi_lookupflags_t (uint32_t bitfield)

Flags determining the method of how paths are resolved.

Used by __wasi_path_filestat_get(), __wasi_path_filestat_set_times(), __wasi_path_link(), and __wasi_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().

Used by __wasi_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.

Possible values:

  • __WASI_PREOPENTYPE_DIR

    Preopened directory.

__wasi_prestat_t (struct)

Information about a preopened resource.

Used by __wasi_fd_prestat_get().

Members:

__wasi_riflags_t (uint16_t bitfield)

Flags provided to __wasi_sock_recv().

Used by __wasi_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, __wasi_fd_fdstat_set_rights(), and __wasi_path_open().

Possible values:

__wasi_roflags_t (uint16_t bitfield)

Flags returned by __wasi_sock_recv().

Used by __wasi_sock_recv().

Possible values:

  • __WASI_SOCK_RECV_DATA_TRUNCATED

    Returned by __wasi_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().

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(). As there are currently no flags defined, it must be set to zero.

Used by __wasi_sock_send().

__wasi_signal_t (uint8_t)

Signal condition.

Used by __wasi_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.

Used by __wasi_subscription_t.

Possible values:

__wasi_subscription_t (struct)

Subscription to an event.

Used by __wasi_poll_oneoff().

Members:

__wasi_timestamp_t (uint64_t)

Timestamp in nanoseconds.

Used by __wasi_filestat_t, __wasi_subscription_t, __wasi_clock_res_get(), __wasi_clock_time_get(), __wasi_fd_filestat_set_times(), and __wasi_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 and __wasi_subscription_t.

__wasi_whence_t (uint8_t)

The position relative to which to set the offset of the file descriptor.

Used by __wasi_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.