Mono Class Library: Mono.Unix.Native.Syscall Overview | Members

Mono.Unix.Native.Syscall.write Method

write writes up to 'count' bytes to the file referenced by the file descriptor 'fileDescriptor' from the buffer starting at 'buf'.

public static long write (int fd, IntPtr buf, ulong count)

See Also

Syscall.fcntl
Syscall.lseek
Syscall.open
Syscall.pipe
Syscall.select

Parameters

fd
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buf
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count
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Returns

Upon successful completion the number of bytes which were written is returned. Otherwise a -1 is returned and the global variable Stdlib.GetLastError is set to indicate the error.

Usage

The write(), writev(), and pwrite() system calls will fail and the file pointer will remain unchanged if:

Error Details
Errno.EBADF

The d argument is not a valid descriptor open for writing.

Errno.EPIPE

An attempt is made to write to a pipe that is not open for reading by any process.

Errno.EPIPE

An attempt is made to write to a socket of type Errno.SOCK_STREAM that is not connected to a peer socket.

Errno.EFBIG

An attempt was made to write a file that exceeds the process's file size limit or the maximum file size.

Errno.EFAULT

Part of iov or data to be written to the file points outside the process's allocated address space.

Errno.EINVAL

The pointer associated with d was negative.

Errno.ENOSPC

There is no free space remaining on the file system containing the file.

Errno.EDQUOT

The user's quota of disk blocks on the file system containing the file has been exhausted.

Errno.EIO

An I/O error occurred while reading from or writing to the file system.

Errno.EINTR

A signal interrupted the write before it could be completed.

Errno.EAGAIN

The file was marked for non-blocking I/O, and no data could be written immediately.

Errno.EROFS

An attempt was made to write over a disk label area at the beginning of a slice. Use disklabel(8) Fl W to enable writing on the disk label area.

In addition, writev() may return one of the following errors:

Error Details
Errno.EDESTADDRREQ

The destination is no longer available when writing to a Ux domain datagram socket on which Syscall.connect(2) had been used to set a destination address.

Errno.EINVAL

The iovcnt argument was less than or equal to 0, or greater than TODO.IOV_MAX .

Errno.EINVAL

One of the iov_len values in the iov array was negative.

Errno.EINVAL

The sum of the iov_len values in the iov array overflowed a 32-bit integer.

Errno.ENOBUFS

The mbuf pool has been completely exhausted when writing to a socket.

The pwrite() system call may also return the following errors:

Error Details
Errno.EINVAL

The offset value was negative.

Errno.ESPIPE

The file descriptor is associated with a pipe, socket, or FIFO.

Remarks

The write() system call attempts to write nbytes of data to the object referenced by the descriptor d from the buffer pointed to by buf . The writev() system call performs the same action, but gathers the output data from the iovcnt buffers specified by the members of the iov array: iov[0], iov[1], ..., iov[iovcnt|-|1]. The pwrite() system call performs the same function, but writes to the specified position in the file without modifying the file pointer.

For writev(), the iovec structure is defined as:

Usage

struct iovec {

};

Each iovec entry specifies the base address and length of an area in memory from which data should be written. The writev() system call will always write a complete area before proceeding to the next.

On objects capable of seeking, the write() starts at a position given by the pointer associated with d , see Syscall.lseek(2) . Upon return from write(), the pointer is incremented by the number of bytes which were written.

Objects that are not capable of seeking always write from the current position. The value of the pointer associated with such an object is undefined.

If the real user is not the super-user, then write() clears the set-user-id bit on a file. This prevents penetration of system security by a user who captures a writable set-user-id file owned by the super-user.

When using non-blocking I/O on objects such as sockets that are subject to flow control, write() and writev() may write fewer bytes than requested; the return value must be noted, and the remainder of the operation should be retried when possible.

Requirements

Namespace: Mono.Unix.Native
Assembly: Mono.Posix (in Mono.Posix.dll)
Assembly Versions: 1.0.5000.0, 2.0.0.0