semantics of fcntl() with l_len being 0

[Kostik Belousov]

On Wed, Aug 26, 2009 at 12:20:57AM -0400, Mikhail T. wrote:
> Hello!
> 
> I'm curious, whether a file, that's locked (via fcntl) with l_start and
> l_len being 0 is supposed to be appendable...
> 
> I would think so, but I notice, that when spamprobe (see mail/spamprobe)
> chews on my spam mailbox, I can not append a new piece of spam to the
> file -- my imap-server is waiting for spamprobe to finish.
> 
> The fcntl(2) says: ``len = 0 means until end of file''. Is that ``until
> the end of file AT THE TIME OF LOCKING'' or simply ``no other lock until
> we are done''? Thanks. Yours,

SUSv3 is definitive on the subject:
A lock shall be set to extend to the largest possible value of the file
offset for that file by setting l_len to 0. If such a lock also has
l_start set to 0 and l_whence is set to SEEK_SET, the whole file shall
be locked.

From sys/kern/kern_lockf.c, line 464:
	} else if (fl->l_len == 0) {
		end = OFF_MAX;

-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 195 bytes
Desc: not available
Url : http://lists.freebsd.org/pipermail/freebsd-fs/attachments/20090826/387a7064/attachment.pgp