sys_write  [fs/read_write.c]

Writes number of bytes to a device (file, socket, etc.) while advancing the file offset position accordingly.


eax 4
ebx Device descriptor.
ecx Pointer to the buffer containing the data to be written.
edx Number of bytes to be written.

Return values

If the system call succeeds the return value is the number of bytes written.
If the system call fails the return value is one of the following errno values:

-EAGAIN Non-blocking I/O has been selected using O_NONBLOCK and the write would block.
-EBADF ebx is not a valid file descriptor or is not open for writing.
-EFAULT ecx is outside your accessible address space.
-EFBIG An attempt was made to write a file that exceeds the implementation-defined maximum file size or the process' file size limit, or to write at a position past the maximum allowed offset.
-EINTR The call was interrupted by a signal before any data was written.
-EINVAL ebx is attached to an object which is unsuitable for writing; or the file was opened with the O_DIRECT flag, and either the address specified in ecx, the value specified in edx, or the current file offset is not suitably aligned.
-EIO A low-level I/O error occurred while modifying the inode.
-ENOSPC The device containing the file referred to by ebx has no room for the data.
-EPIPE ebx is connected to a pipe or socket whose reading end is closed. When this happens the writing process will also receive a SIGPIPE signal. (Thus, the write return value is seen only if the program catches, blocks or ignores this signal.)


A successful return from sys_write does not make any guarantee that data has been committed to disk. In fact, on some buggy implementations, it does not even guarantee that space has successfully been reserved for the data. The only way to be sure is to call sys_fsync after you are done writing all your data.