linux: Require /dev/shm as the shared memory file system

Previously, glibc would pick an arbitrary tmpfs file system from
/proc/mounts if /dev/shm was not available.  This could lead to
an unsuitable file system being picked for the backing storage for
shm_open, sem_open, and related functions.

This patch introduces a new function, __shm_get_name, which builds
the file name under the appropriate (now hard-coded) directory.  It is
called from the various shm_* and sem_* function.  Unlike the
SHM_GET_NAME macro it replaces, the callers handle the return values
and errno updates.  shm-directory.c is moved directly into the posix
subdirectory because it can be implemented directly using POSIX
functionality.  It resides in libc because it is needed by both
librt and nptl/htl.

In the sem_open implementation, tmpfname is initialized directly
from a string constant.  This happens to remove one alloca call.

Checked on x86_64-linux-gnu.

1 files changed, 2 insertions, 1 deletions

diff --git a/posix/Makefile b/posix/Makefile
index 956ef7d397..f54015b9a8 100644
--- a/posix/Makefile
+++ b/posix/Makefile
@@ -65,7 +65,8 @@ routines :=								      \
 	spawnattr_setsigmask spawnattr_setschedpolicy spawnattr_setschedparam \
 	posix_madvise							      \
 	get_child_max sched_cpucount sched_cpualloc sched_cpufree \
-	streams-compat
+	streams-compat \
+	shm-directory
 
 aux		:= init-posix environ
 tests		:= test-errno tstgetopt testfnm runtests runptests \