sys_read [fs/read_write.c]
Reads number of bytes from a device (file, socket, etc.) while advancing the file position accordingly. Arguments
eax | 3
ebx | Device descriptor.
ecx | Pointer to the buffer that will receive the data.
edx | Number of bytes to be read.
Return values If the system call succeeds the return value is the number of bytes read. 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 no data was immediately available for reading.`
`-EBADF` | `ebx is not a valid file descriptor or is not open for reading.`
`-EFAULT` | `ecx is outside your accessible address space.`
`-EINTR` | `The call was interrupted by a signal before any data was read.`
`-EINVAL` | `ebx is attached to an object which is unsuitable for reading; 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` | `I/O error. This will happen for example when the process is in a background process group, tries to read from its controlling tty, and either it is ignoring or blocking SIGTTIN or its process group is orphaned. It may also occur when there is a low-level I/O error while reading from a disk or tape.`
`-EISDIR` | `ebx refers to a directory.`
Remarks On success, the return value may be smaller than the number of bytes requested; this may happen for example because fewer bytes are actually available right now (maybe because we were close to end-of-file, or because we are reading from a pipe, or from a terminal), or because sys_read was interrupted by a signal. On NFS file systems, reading small amounts of data will only update the time stamp the first time, subsequent calls may not do so. This is caused by client side attribute caching, because most if not all NFS clients leave st_atime (last file access time) updates to the server and client side reads satisfied from the client's cache will not cause st_atime updates on the server as there are no server side reads. UNIX semantics can be obtained by disabling client side attribute caching, but in most situations this will substantially increase server load and decrease performance. Many filesystems and disks were considered to be fast enough that the implementation of O_NONBLOCK was deemed unnecessary. So, O_NONBLOCK may not be available on files and/or disks. Compatibility n/a