SysV IPC: shmctl/msgctl/semctl returns EIDRM instead of EINVAL

[Anton Arapov <aarapov@redhat.com>]

Hi!

  SysV code returns EIDRM for collision of IDs. I sure it should return EINVAL.

  Steps to reproduce: (this for shared memory code, for msg/sem it is the same)
   1. Create then drop 2 shmem segments, then create a third.
   2. Try to shmctl(IPC_STAT) the two now-invalid shm IDs.
   3. Note error codes returned.

   One call gives EINVAL, one gives EIDRM due to collision with the third shmem segment.
   Should both give EINVAL, this is what I've got on every other Unix I've tried it on. 

  IPC code is good, EIDRM is justification of EINVAL. But neither SVr4 nor SVID documents EIDRM. 
  Single Unix Specification mentions EINVAL but not EIDRM as a possible failure for shmctl(), so the current kernel behavior is not merely self-inconsistent but a flat violation of the spec. 

  Can somebody explain why do we have EIDRM?

Anton.
SUS: http://www.opengroup.org/onlinepubs/007908799/xsh/shmctl.html

Attachment: shmctl-bug.c
Description: bug_reproducer