Hello Jens, Thanks for this very thorough report! On 2/16/09, Jens Thoms Toerring <jt@xxxxxxxxxxx> wrote: > Dear Michael, > > I have here two small patches for the man pages sem_open(3) > and sem_overview(7). They result from a recent discussion in > c.o.l.d.a where someone had problems creating a named semaphore > using a name of "/tmp/somename". From the man pages it's not > absolutely clear that this isn't allowed. Agreed. > Moreover, one gets an > errno of ENOENT in this case which doesn't seem to be covered > in sem_open(3). Thus I made a modification in sem_overview(7) > so that it now says that slashes embedded into to the name are > not allowed and to sem_open(3) to say that ENOENT can also be > the result of having O_CREAT set in oflag but using an invalid > name. See my comments below. > The actual situation is a bit more complicated as a look at > the glibc code for sem_open() shows (you can actually use a slash > in the name, e.g. "/aaa/bbb", but then a directory named sem.aaa > you have write permissions for must already exist in /dev/shm, > moreover, the slash at the start isn't needed). Thanks for filling in that background. My reading of the glibc source, plus testing, confirms what you say. > But I guess that > isn't of much relevance to the user and probably is better left > untold since putting it into writing might make it more difficult > to change the behaviour later on. Indeed, this is best left untold, since it's non-standard, non-portable behavior that could change. > Here's the diff for sem_overview(7): > > ----------8<------------------------------------------------------ > --- sem_overview.7 2009-02-09 03:14:25.000000000 +0100 > +++ sem_overview.7.new 2009-02-15 18:40:48.000000000 +0100 > @@ -48,6 +48,9 @@ > Two processes can operate on the same named semaphore by passing > the same name to > .BR sem_open (3). > +Note that > +.IR /somename > +may not contain slashes except the required one at the very start. In fact, I made a bigger fix, stating: A named semaphore is identified by a name of the form /somename; that is, a null-terminated string of up to NAME_MAX+1 (i.e., 256) characters consisting of an initial slash, followed by one or more characters, none of which are slashes. > The > .BR sem_open (3) > @@ -113,7 +116,7 @@ > normally mounted under > .IR /dev/shm , > with names of the form > -.IR \fBsem.\fPname . > +.IR \fBsem.\fPsomename . Yep -- made that change. > Since Linux 2.6.19, ACLs can be placed on files under this directory, > to control object permissions on a per-user and per-group basis. > ----------8<------------------------------------------------------ > > and here's the one for sem_open(3): > > ----------8<------------------------------------------------------ > --- sem_open.3 2009-02-09 03:14:20.000000000 +0100 > +++ sem_open.3.new 2009-02-15 18:46:11.000000000 +0100 > @@ -149,10 +149,17 @@ > The > .B O_CREAT > flag was not specified in > -.IR oflag , > +.IR oflag > and no semaphore with this > .I name > -exists. > +exists, or the > +.B O_CREAT > +flag > +was set in > +.IR oflag > +but > +.I name > +wasn't well-formed. I applied this change, with slight edits. The changes will be in man-pages-3.19. In fact, your report also caused me to look at the pages for POSIX message queues and shared memory, and make analogous changes there (mq_overview.7, mq_open.3, shm_open.3). Thanks very much! Michael -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ git://git.kernel.org/pub/scm/docs/man-pages/man-pages.git man-pages online: http://www.kernel.org/doc/man-pages/online_pages.html Found a bug? http://www.kernel.org/doc/man-pages/reporting_bugs.html -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
