| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <4DB1697B.10606@redhat.com>
Date: Fri, 22 Apr 2011 05:41:47 -0600
From: Eric Blake <eblake@...hat.com>
To: Josef Bacik <josef@...icpanda.com>
CC: linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] fs: add SEEK_HOLE and SEEK_DATA flags
On 04/21/2011 07:22 PM, Josef Bacik wrote:
>> You absolutely need to match Solaris semantics, which are documented as follows:
>>
>> � If whence is SEEK_HOLE, the offset of the start of the next hole
>> greater than or equal to the supplied offset is returned. The def-
>> inition of a hole is provided near the end of the DESCRIPTION.
>>
>> Note that in that definition, SEEK_HOLE does _not_ reposition the file offset
>> (it returns the offset of the next hole, which might be at the end of the file
>> since all files have a virtual hole at the end, but leaves the position
>> unchanged). I'd have to write a test program on Solaris to see whether that
>> definition is actually true, or if it is a bug in the Solaris man page.
>
> lseek's purpose is to reposition the file position, so I'd imagine
> this is just a bug in the man page.
Confirmed that the Solaris man page is buggy and does not accurately
describe the semantics that are actually implemented. My testing showed:
lseek(fd, off, SEEK_HOLE) has four cases:
off < end, in data: repositions to the next hole as if by lseek(fd,
next_hole, SEEK_CUR); the next hole is guaranteed to exist, even if at
end of file
off < end, in hole, and later in file has data: repositions as if by
lseek(fd, off, SEEK_CUR)
off < end, in hole, and no further data in file: repositions as if by
lseek(fd, 0, SEEK_END)
off == end: fails with ENXIO
lseek(fd, off, SEEK_DATA) has four cases:
off < end, in data: repositions as if by lseek(fd, off, SEEK_CUR)
off < end, in hole, and later in file has data: repositions to the next
data as if by lseek(fd, next_data, SEEK_CUR)
off < end, in hole, and remainder of file is hold: fails with ENXIO
off == end: fails with ENXIO
Here's how I tested:
$ uname -sr
SunOS 5.10
$ cat foo.c
#include <unistd.h>
#include <stdio.h>
#include <errno.h>
#include <fcntl.h>
#include <string.h>
static int
make_sparse (const char *name)
{
int fd = open (name, O_RDWR | O_CREAT | O_TRUNC, 0600);
if (fd < 0)
return fd;
printf ("creating %s\n", name);
if (write (fd, "a", 1) != 1)
goto cleanup;
if (lseek (fd, 1024*1024, SEEK_CUR) == -1)
goto cleanup;
if (write (fd, "b", 1) != 1)
goto cleanup;
if (lseek (fd, 0, SEEK_SET) != 0)
goto cleanup;
return fd;
cleanup:
close (fd);
return -1;
}
int
main (int argc, char **argv)
{
off_t off;
off_t end;
int fd = argc > 2 ? open (argv[1], O_RDONLY)
: make_sparse (argc > 1 ? argv[1] : "file");
perror(NULL);
if (fd < 0)
return 2;
printf ("fpathconf gives %ld, ENXIO is %d\n",
fpathconf (fd, _PC_MIN_HOLE_SIZE), ENXIO);
puts ("\ntesting at start");
errno = 0;
off = lseek (fd, 0, SEEK_CUR);
printf ("CUR at offset %lld, errno %d\n", (long long) off, errno);
errno = 0;
off = lseek (fd, 0, SEEK_HOLE);
printf ("HOLE gives offset %lld, errno %d\n", (long long) off, errno);
errno = 0;
off = lseek (fd, 0, SEEK_CUR);
printf ("CUR at offset %lld, errno %d\n", (long long) off, errno);
errno = 0;
off = lseek (fd, 0, SEEK_DATA);
printf ("DATA gives offset %lld, errno %d\n", (long long) off, errno);
errno = 0;
off = lseek (fd, 0, SEEK_CUR);
printf ("CUR at offset %lld, errno %d\n", (long long) off, errno);
errno = 0;
off = lseek (fd, 0, SEEK_HOLE);
printf ("HOLE gives offset %lld, errno %d\n", (long long) off, errno);
errno = 0;
off = lseek (fd, 0, SEEK_CUR);
printf ("CUR at offset %lld, errno %d\n", (long long) off, errno);
puts ("\ntesting at end");
errno = 0;
off = end = lseek (fd, 0, SEEK_END);
printf ("end at offset %lld, errno %d\n", (long long) off, errno);
errno = 0;
off = lseek (fd, end, SEEK_HOLE);
printf ("HOLE gives offset %lld, errno %d\n", (long long) off, errno);
errno = 0;
off = lseek (fd, 0, SEEK_CUR);
printf ("CUR at offset %lld, errno %d\n", (long long) off, errno);
errno = 0;
off = lseek (fd, end, SEEK_DATA);
printf ("DATA gives offset %lld, errno %d\n", (long long) off, errno);
errno = 0;
off = lseek (fd, 0, SEEK_CUR);
printf ("CUR at offset %lld, errno %d\n", (long long) off, errno);
errno = 0;
off = lseek (fd, end - 1, SEEK_HOLE);
printf ("HOLE gives offset %lld, errno %d\n", (long long) off, errno);
errno = 0;
off = lseek (fd, 0, SEEK_CUR);
printf ("CUR at offset %lld, errno %d\n", (long long) off, errno);
errno = 0;
off = lseek (fd, end - 1, SEEK_DATA);
printf ("DATA gives offset %lld, errno %d\n", (long long) off, errno);
errno = 0;
off = lseek (fd, 0, SEEK_CUR);
printf ("CUR at offset %lld, errno %d\n", (long long) off, errno);
puts ("\ntesting at offset 1");
errno = 0;
off = lseek (fd, 1, SEEK_HOLE);
printf ("HOLE gives offset %lld, errno %d\n", (long long) off, errno);
errno = 0;
off = lseek (fd, 0, SEEK_CUR);
printf ("CUR at offset %lld, errno %d\n", (long long) off, errno);
errno = 0;
off = lseek (fd, 1, SEEK_DATA);
printf ("DATA gives offset %lld, errno %d\n", (long long) off, errno);
errno = 0;
off = lseek (fd, 0, SEEK_CUR);
printf ("CUR at offset %lld, errno %d\n", (long long) off, errno);
puts ("\ntesting at offset 200000");
errno = 0;
off = lseek (fd, 200000, SEEK_HOLE);
printf ("HOLE gives offset %lld, errno %d\n", (long long) off, errno);
errno = 0;
off = lseek (fd, 0, SEEK_CUR);
printf ("CUR at offset %lld, errno %d\n", (long long) off, errno);
errno = 0;
off = lseek (fd, 200000, SEEK_DATA);
printf ("DATA gives offset %lld, errno %d\n", (long long) off, errno);
errno = 0;
off = lseek (fd, 0, SEEK_CUR);
printf ("CUR at offset %lld, errno %d\n", (long long) off, errno);
if (close (fd))
return 3;
return 0;
}
$ ./foo
creating file
Error 0
fpathconf gives 512, ENXIO is 6
testing at start
CUR at offset 0, errno 0
HOLE gives offset 131072, errno 0
CUR at offset 131072, errno 0
DATA gives offset 0, errno 0
CUR at offset 0, errno 0
HOLE gives offset 131072, errno 0
CUR at offset 131072, errno 0
testing at end
end at offset 1048578, errno 0
HOLE gives offset -1, errno 6
CUR at offset 1048578, errno 0
DATA gives offset -1, errno 6
CUR at offset 1048578, errno 0
HOLE gives offset 1048578, errno 0
CUR at offset 1048578, errno 0
DATA gives offset 1048577, errno 0
CUR at offset 1048577, errno 0
testing at offset 1
HOLE gives offset 131072, errno 0
CUR at offset 131072, errno 0
DATA gives offset 1, errno 0
CUR at offset 1, errno 0
testing at offset 200000
HOLE gives offset 200000, errno 0
CUR at offset 200000, errno 0
DATA gives offset 1048576, errno 0
CUR at offset 1048576, errno 0
$ gtruncate -s 1M sparse
$ ./foo sparse 2
Error 0
fpathconf gives 512, ENXIO is 6
testing at start
CUR at offset 0, errno 0
HOLE gives offset 0, errno 0
CUR at offset 0, errno 0
DATA gives offset -1, errno 6
CUR at offset 0, errno 0
HOLE gives offset 0, errno 0
CUR at offset 0, errno 0
testing at end
end at offset 1048576, errno 0
HOLE gives offset -1, errno 6
CUR at offset 1048576, errno 0
DATA gives offset -1, errno 6
CUR at offset 1048576, errno 0
HOLE gives offset 1048576, errno 0
CUR at offset 1048576, errno 0
DATA gives offset -1, errno 6
CUR at offset 1048576, errno 0
testing at offset 1
HOLE gives offset 1, errno 0
CUR at offset 1, errno 0
DATA gives offset -1, errno 6
CUR at offset 1, errno 0
testing at offset 200000
HOLE gives offset 1048576, errno 0
CUR at offset 1048576, errno 0
DATA gives offset -1, errno 6
CUR at offset 1048576, errno 0
$
--
Eric Blake eblake@...hat.com +1-801-349-2682
Libvirt virtualization library http://libvirt.org
Download attachment "signature.asc" of type "application/pgp-signature" (620 bytes)
Powered by blists - more mailing lists