Messages in this thread | | | Subject | Re: [PATCH] fs/locks.c fcntl_setlease did not check if a file was opened for writing before granting a read lease | From | Sean Neakums <> | Date | Tue, 02 Dec 2003 10:53:05 +0000 |
| |
Jamie Lokier <jamie@shareable.org> writes:
> To detect if anyone has the file open for writing, you'll a new count > field which keeps track of writer references. Something like this: > > if ((arg == F_RDLCK) > && ((atomic_read(&inode->i_writer_count) != 0))) > > You'll also need to modify all the places where that needs to be > maintained.
Looking at 2.6.0-test11, it seems that its struct inode has such a field, albeit named i_writecount. Commentary from fs/namei.c:
/* * get_write_access() gets write permission for a file. * put_write_access() releases this write permission. * This is used for regular files. * We cannot support write (and maybe mmap read-write shared) accesses and * MAP_DENYWRITE mmappings simultaneously. The i_writecount field of an inode * can have the following values: * 0: no writers, no VM_DENYWRITE mappings * < 0: (-i_writecount) vm_area_structs with VM_DENYWRITE set exist * > 0: (i_writecount) users are writing to the file. * * Normally we operate on that counter with atomic_{inc,dec} and it's safe * except for the cases where we don't hold i_writecount yet. Then we need to * use {get,deny}_write_access() - these functions check the sign and refuse * to do the change if sign is wrong. Exclusion between them is provided by * spinlock (arbitration_lock) and I'll rip the second arsehole to the first * who will try to move it in struct inode - just leave it here. */ - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |