Mail Archives: cygwin-developers/2000/04/03/12:31:56
Chris Faylor wrote:
>
> On Sun, Apr 02, 2000 at 09:20:45PM -0400, Chris Faylor wrote:
> >I can't see an easy fix for this behavior other than to detect an
> >ERROR_ACCESS_DENIED in _read and then attempt to see if we're at EOF.
> >In this case, we'd have to figure out how many bytes are actually left
> >in the file and just pass that many to ReadFile. That could still fail,
> >of course, but in that case, it would be a UNIX-type failure.
>
> On second thought, this isn't feasible either. We actually have to figure
> out how many bytes are actually valid (x) in the buffer and how many bytes
> would be read in (y). If y <= x then the read should succeed.
>
> Corinna, do you want to take a shot at fixing this? I think the correct
> place to do this is probably in fhandler_disk_file::read since you can't
> really determine the number of bytes remaining anywhere else, can you?
>
> Maybe to be safe we need a new fhandler method which can be triggered to
> restart a read in the above scenario. So it would be something like:
> [...]
Should be no problem to do so, but I still wonder why this should be
needed. I have checked this out on my linux box (2.2.13 kernel,
glibc-2):
=== SNIP ===
#include <sys/types.h> etcetera...
...
int
main(int argc, char** argv)
{
int fd;
char buf1[64000];
ssize_t bytes;
if ((fd = open (argv[1] ? argv[1] : argv[0], O_RDONLY)) < 0)
return 0;
lseek (fd, (off_t) 0, SEEK_END);
bytes = read (fd, buf1 + 64000, 40000);
printf ("read: %d, err: %d, %s\n", bytes, errno, strerror(errno));
close (fd);
return 0;
}
=== SNAP ===
and the message is
read: -1, err: 14, Bad address <=== EFAULT!
as it's currently under cygwin, too, and it _is_ an UNIX-style error.
This is documented in the linux read(2) man page as well.
So, if this behaviour is the same in a "reference os", where is
the problem??? Well, uhm, I have no copy of POSIX, obviously...
Corinna
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