Package: smbfs Version: 1:3.0.28a-3 Severity: normal -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1
In http://bugs.debian.org/483502, i wrote: > locking a certain range of a file with a read lock and then locking > the same range with a write lock gives an error when a CIFS share is > mounted with "brl". This doesn't make much sense to me, but i'm > willing to accept it as intended for now. After doing more reading, it still doesn't make sense: the filesystem is behaving with non-POSIX semantics, which causes breakage in other packages (for example, see http://bugs.debian.org/483216). In particular, the semantics specified by fcntl(2) for setting a lock state: A single process can hold only one type of lock on a file region; if a new lock is applied to an already-locked region, then the existing lock is converted to the new lock type. (this appears to be true for both advisory *and* mandatory locks) However, when accessing a CIFS share mounted with with "brl" (standard CIFS-style server-side byte-range locking), converting a read lock to a write lock gives a "permission denied" error. The same error does *not* occur when using the CIFS share mounted with "nobrl", or when attempting the same series of operations against a tmpfs (whether or not the tmpfs is mounted with -o mand). Shouldn't mount.cifs do its best to mimic the expected semantics of fcntl(F_SETLK) using the underlying CIFS semantics? If CIFS has no explicit lock upgrade/downgrade operations, as long as the protocol is capable of dropping a lock and acquiring a new one, these two primitives used in sequence could be used to emulate a lock upgrade/downgrade. Attached is the test program that displays this behavior. It should fail with "write lock failed: Permission denied" when used on a file on a CIFS mount, and it has succeeded quietly on every other filesystem i've tried. the latest version of the source can be found at http://cmrg.fifthhorseman.net/browser/trunk/test/testlocking/testlocking.c Thanks for maintaining samba in debian! Regards, --dkg - -- System Information: Debian Release: lenny/sid APT prefers testing APT policy: (500, 'testing'), (200, 'unstable'), (101, 'experimental') Architecture: i386 (i686) Kernel: Linux 2.6.24-1-686 (SMP w/1 CPU core) Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8) Shell: /bin/sh linked to /bin/bash Versions of packages smbfs depends on: ii libc6 2.7-10 GNU C Library: Shared libraries ii netbase 4.32 Basic TCP/IP networking system ii samba-common 1:3.0.28a-3 Samba common files used by both th smbfs recommends no packages. - -- no debconf information -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.6 (GNU/Linux) iQIVAwUBSD47NszS7ZTSFznpAQIv4A/+O3ofw/kIzXJuvtertKI2nPqcsiOT27Fl Pf7f1Mp+qhEeVrbZ6ESZA1SSuHBeT7JKYurrsw/z7y2D6nuapqqR6DXihj9QdbIi gZoHZhVH1tCDeuAv9pR8avV8QHXcE8BSu0vZQuaMI/zLbkxln4qbDCtOPvAmowfr vBIKsE9Zb/hYdFCkdYP2lYGXVfTlZo26JMNKsrA+jezLk1xBPmT/UtpvD1L//19+ CNlPfTqsqAksFAqLD6TLUVgLeNv1MiMGEj9sOGiGuDXvixeCcGleemQkmbKm/ihl viXBHYh2M9ZZtKU3I2R0tnKrwCnL1ZsU/QQb70/d3fKhJeoQrsd9jgnS0jeArLLy RwTSWnvj1WcxId0+JT4nL6gvRNLs64fyI6QzZ/6eLHrPBQtRxEf055I2UvjO81tE n9YA0nfIxeyeGc1+XqnE4FUmY0LEhuJT48PbsrHP5WT4XCb3mIhKg42EJ+r6WQIn G8I0TzMZsDxXZ6vYnd4BfNKhpf0qSn2CoEcj1Jtg4lovLltc5j0VWji4iuXaLiJ3 o5rao7F0yk12iomSE2XE7gIwU7YUOHGzcqx011cDNmv/z2Vdr8tFCB8Svh7Y6VMA 0LcDH8LLVGSlXneP5frzUimBS1A6ogu8ocYxhIp4ww60Lqq1TOOIebj2m/znaaj4 CWuXI6GnK+w= =y3y4 -----END PGP SIGNATURE-----
/* grep open(2) for O_LARGEFILE to explain this: */ #define _FILE_OFFSET_BITS 64 #include <sys/types.h> #include <sys/stat.h> #include <unistd.h> #include <fcntl.h> #include <stdio.h> /* Author: Daniel Kahn Gillmor <[EMAIL PROTECTED]> Date: 2008-05-28 This is a demonstration program for testing http://bugs.debian.org/483216 */ int main(int argc, char* argv[]) { struct flock flock; int fd; flock.l_whence=SEEK_SET; /* open file, get file descriptor */ fd = open(argv[1], O_RDWR|O_CREAT, 0644); fcntl(fd, F_SETFD, FD_CLOEXEC | fcntl(fd, F_GETFD)); /* get read lock: */ flock.l_type=F_RDLCK; flock.l_start=0; flock.l_len = 1; if (0 != fcntl(fd, F_SETLK64, &flock)) { perror("read lock failed"); return 1; } /* get write lock for same range: */ flock.l_type=F_WRLCK; if (0 != fcntl(fd, F_SETLK64, &flock)) { /* fails here when used on CIFS share mounted without nobrl option */ perror("write lock failed"); return 1; } return 0; }
