Function preadv [src]
Number of bytes read is returned. Upon reading end-of-file, zero is returned.
Retries when interrupted by a signal.
For POSIX systems, if fd is opened in non blocking mode, the function will
return error.WouldBlock when EAGAIN is received.
On Windows, if the application has a global event loop enabled, I/O Completion Ports are
used to perform the I/O. error.WouldBlock is not possible on Windows.
This operation is non-atomic on the following systems:
Darwin
Windows
On these systems, the read races with concurrent writes to the same file descriptor.
Prototype
pub fn preadv(fd: fd_t, iov: []const iovec, offset: u64) PReadError!usize Parameters
fd: fd_tiov: []const iovecoffset: u64 Possible Errors
In WASI, this error occurs when the file descriptor does not hold the required rights to read from it.
reading a timerfd with CANCEL_ON_SET will lead to this error when the clock goes through a discontinuous change
Unable to read file due to lock.
This error occurs in Linux if the process to be read from no longer exists.
The Operating System returned an undocumented error code.
This error is in theory not possible, but it would be better to handle this error than to invoke undefined behavior.
When this error code is observed, it usually means the Zig Standard Library needs a small patch to add the error code to the error set for the respective function.
This error occurs when no global event loop is configured, and reading from the file descriptor would block.
Source
pub fn preadv(fd: fd_t, iov: []const iovec, offset: u64) PReadError!usize {
const have_pread_but_not_preadv = switch (native_os) {
.windows, .macos, .ios, .watchos, .tvos, .visionos, .haiku => true,
else => false,
};
if (have_pread_but_not_preadv) {
// We could loop here; but proper usage of `preadv` must handle partial reads anyway.
// So we simply read into the first vector only.
if (iov.len == 0) return 0;
const first = iov[0];
return pread(fd, first.base[0..first.len], offset);
}
if (native_os == .wasi and !builtin.link_libc) {
var nread: usize = undefined;
switch (wasi.fd_pread(fd, iov.ptr, iov.len, offset, &nread)) {
.SUCCESS => return nread,
.INTR => unreachable,
.INVAL => unreachable,
.FAULT => unreachable,
.AGAIN => unreachable,
.BADF => return error.NotOpenForReading, // can be a race condition
.IO => return error.InputOutput,
.ISDIR => return error.IsDir,
.NOBUFS => return error.SystemResources,
.NOMEM => return error.SystemResources,
.NOTCONN => return error.SocketNotConnected,
.CONNRESET => return error.ConnectionResetByPeer,
.TIMEDOUT => return error.ConnectionTimedOut,
.NXIO => return error.Unseekable,
.SPIPE => return error.Unseekable,
.OVERFLOW => return error.Unseekable,
.NOTCAPABLE => return error.AccessDenied,
else => |err| return unexpectedErrno(err),
}
}
const preadv_sym = if (lfs64_abi) system.preadv64 else system.preadv;
while (true) {
const rc = preadv_sym(fd, iov.ptr, @min(iov.len, IOV_MAX), @bitCast(offset));
switch (errno(rc)) {
.SUCCESS => return @bitCast(rc),
.INTR => continue,
.INVAL => unreachable,
.FAULT => unreachable,
.NOENT => return error.ProcessNotFound,
.AGAIN => return error.WouldBlock,
.BADF => return error.NotOpenForReading, // can be a race condition
.IO => return error.InputOutput,
.ISDIR => return error.IsDir,
.NOBUFS => return error.SystemResources,
.NOMEM => return error.SystemResources,
.NOTCONN => return error.SocketNotConnected,
.CONNRESET => return error.ConnectionResetByPeer,
.TIMEDOUT => return error.ConnectionTimedOut,
.NXIO => return error.Unseekable,
.SPIPE => return error.Unseekable,
.OVERFLOW => return error.Unseekable,
else => |err| return unexpectedErrno(err),
}
}
}