shm_open doesn't work (fix maybe).

I have been chasing all around trying to find out why shm_open always returns ENOSYS. It is implemented in glibc-2.2.2, and seems the 2.4.3 kernel knows about shmfs.

It seems the file linux/mm/shmem.c has:

    #define SHMEM_MAGIC 0x01021994

And the glibc-2.2.2/sysdeps/unix/sysv/linux/linux_fsinfo.h has:

    #define SHMFS_SUPER_MAGIC 0x02011994

Well, which is correct?

Looking for (trouble?) the reason, I found a patch
http://www.mail-archive.com/[email protected]/msg16996.html

where there seems to be a typo, the remove line is correct:
-#define SHM_FS_MAGIC 0x02011994

but the insert line has the 0201 reversed:
+#define SHMEM_MAGIC 0x01021994

Has anyone else run into this? (It seems the documentation on shmfs is sparse, so I don't think too many folks are even messing with it).

Initially I thought, hey simple, just fix the kernel source, and everyone will be happy. But, then I thought, ooof! code I build for someone without a patched kernel will surely break. So then I thought simple I'll fix glibc and statically link. Of course, then someone will fix this, and all my binaries will be broken.

Help! what is the "right" fix.

Update your glibc, 2.2.3pre* matches 2.4.x kernel:

2001-03-03 Ulrich Drepper <[email protected]>

* sysdeps/unix/sysv/linux/linux_fsinfo.h (SHMFS_SUPER_MAGIC):
Update for real 2.4 kernels.

Jakub

Hi,

Yes, and I apologize to Ulrich that the changed number slipped through to the official kernel. My fault.

Greetings
Christoph