Date: Fri, 13 Dec 2002 09:28:44 -0800 From: Joe Kelsey <joek@mail.flyingcroc.net> To: freebsd-current@freebsd.org Subject: Re: Posix Semaphores in -CURRENT Message-ID: <3DFA18CC.8090205@mail.flyingcroc.net> References: <3DF8F08E.8050809@mail.flyingcroc.net> <3DFA0771.BDFC87A8@mindspring.com> <3DFA0DAC.2070801@mail.flyingcroc.net> <3DFA1251.C4755C5B@mindspring.com>
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Terry Lambert wrote:
> Get me the exact file you are concerned about, and I will stare
> at it with you. I think, though, that if there is a problem, it's
> just that you are catching things in mid-implementation (POSIX
> semaphores were supported in the other scope, but not system,
> until very recently; there's even magic POSIX manifests that tell
> you not to use them).
src/sys/kern/uipc_sem.c, version 1.3:
...
#define SEM_MAX_NAMELEN 14
...
static int
sem_create(td, name, ksret, mode, value)
...
if (value > SEM_VALUE_MAX)
return (EINVAL);
ret = malloc(sizeof(*ret), M_SEM, M_WAITOK | M_ZERO);
if (name != NULL) {
len = strlen(name);
if (len > SEM_MAX_NAMELEN) {
free(ret, M_SEM);
return (ENAMETOOLONG);
}
/* name must start with a '/' but not contain one. */
if (*name != '/' || len < 2 || index(name + 1, '/') != NULL) {
free(ret, M_SEM);
return (EINVAL);
}
The comment makes it look like this code allows a 14-character named
semaphore which *must* start with a slash and cannot contain embedded
slashes. In other words, it does *not* conform to pathname semantics.
If some other part of the system already verifies that the named
semaphore is actually an empty directory entry, then why is there a name
length restriction and why is there a '/' check?
If this is a bug, I will happily submit a PR. I wanted some feedback
before doing so. I am interested in playing with the semantics of posix
semaphores. It looks to me as though they could be implemented more
resource-efficiently than SVID semaphores and really do have different
semantics. I really want to try to understand what will and won't be
released in 5.0. How will I enable these for testing/use and will they
work in a portable way? The only way to answer those questions right
now is to examine the source. I am trying to understand the source,
especially in how it may or may not restrict use of semaphores.
/Joe
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