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readwrite function in libc
- To: <ecos-discuss at sources dot redhat dot com>
- Subject: [ECOS] readwrite function in libc
- From: "james chen" <james_ch1 at sina dot com>
- Date: Tue, 19 Jun 2001 10:46:27 +0800
Hi,
in the function of readwrite ( io\fileio\current\src\io.cxx)
{
...
LOCK_FILE( fp );
ret = op( fp, &uio );
UNLOCK_FILE( fp );
cnt -= uio.uio_resid;
cyg_fp_free( fp );
CYG_CANCELLATION_POINT;
FILEIO_RETURN_VALUE(cnt);
}
if ret is not equal ENOERR, this may not compatible with read() standard. Is
there a bug in it:-)
Best Regards,
james
----------------------------------------------------------------------------
--------------------------
read - read from a file descriptor
#include <unistd.h>
ssize_t read(int fd, void *buf, size_t count );
DESCRIPTION
read() attempts to read up to count bytes from file descriptor fd
into the buffer starting at buf. If count is zero, read()returns zero
and has no other results. If count is greater than SSIZE_MAX, the
result is unspecified.
RETURN VALUE
On success, the number of bytes read is returned (zero indicates end of
file), and the file position is advanced by this number.
It is not an error if this number is 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
read()was interrupted by a signal. On error, -1 is returned, and
errno is set appropriately. In this case it is left unspecified whether
the file position (if any) changes.
ERRORS
EINTR
The call was interrupted by a signal before any data was read.
EAGAIN
Non-blocking I/O has been selected using
O_NONBLOCK
and no data was immediately available for reading.
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
fd refers to a directory.
EBADF
fd is not a valid file descriptor or is not open for reading.
EINVAL
fd is attached to an object which is unsuitable for reading.
EFAULT
buf is outside your accessible address space. Other errors may
occur, depending on the object connected to fd. POSIX allows a
read that is interrupted after reading some data to return -1
(with errno set to EINTR) or to return the number of bytes
already read.