sem_open(2) and ENAMETOOLONG

[Kamil Rytarowski <n54%gmx.com@localhost>]

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The sem_open(2) function call reports an error for a too long name and
sets errno:

[ENAMETOOLONG]     The name argument is too long.

I noted in the kernel that the limit is SEM_MAX_NAMELEN:

do_ksem_open(struct lwp *l, const char *semname, int oflag, mode_t mode,
     unsigned int value, intptr_t *idp, copyout_t docopyout)
{
        char name[SEM_MAX_NAMELEN + 1];
        proc_t *p = l->l_proc;
        ksem_t *ksnew = NULL, *ks;
        file_t *fp;
        intptr_t id;
        int fd, error;

        error = copyinstr(semname, name, sizeof(name), NULL);
        if (error) {
                return error;
        }

 -- sys/kern/uipc_sem.c

The limit is held privately in the kernel:

sys/kern/uipc_sem.c:#define     SEM_MAX_NAMELEN         14

I read in the POSIX resources that the limit is defined by PATH_MAX or
its variation:

ENAMETOOLONG
    The length of the name argument exceeds {PATH_MAX} or a pathname
component is longer than {NAME_MAX}.

 -- https://man-k.org/man/posix/3P/sem_open?r=1&q=sem_open

[ENAMETOOLONG]
    The length of the name argument exceeds {_POSIX_PATH_MAX} on
systems that do not support the XSI option [XSI] [Option Start]  or
exceeds {_XOPEN_PATH_MAX} on XSI systems, [Option End]  or has a
pathname component that is longer than {_POSIX_NAME_MAX} on systems
that do not support the XSI option [XSI] [Option Start]  or longer
than {_XOPEN_NAME_MAX} on XSI systems. [Option End]

 --
http://pubs.opengroup.org/onlinepubs/9699919799/functions/sem_open.html

Is our code compliant? If so, could we export SEM_MAX_NAMELEN to
userland header.


MacOSX defines SEM_NAME_LEN as 31.
https://developer.apple.com/library/ios/documentation/System/Conceptual/
ManPages_iPhoneOS/man2/sem_open.2.html


Additionally I noted that SEM_VALUE_MAX is defined at least twice in
the code-base, in <semaphore.h> and sys/kern/uipc_sem.c (thankfully
with the same value: ~0U).

FreeBSD seems to respect the PATH_MAX property of the name argument:

sem_t *
_sem_open(const char *name, int flags, ...)
{
	char path[PATH_MAX];
/***/

 --
https://github.com/freebsd/freebsd/blob/af3e10e5a78d3af8cef6088748978c6c
612757f0/lib/libc/gen/sem_new.c#L158
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