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ipc: add sysctl to specify desired next object id

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Add 3 new variables and sysctls to tune them (by one "next_id" variable
for messages, semaphores and shared memory respectively).  This variable
can be used to set desired id for next allocated IPC object.  By default
it's equal to -1 and old behaviour is preserved.  If this variable is
non-negative, then desired idr will be extracted from it and used as a
start value to search for free IDR slot.

Notes:

1) this patch doesn't guarantee that the new object will have desired
   id.  So it's up to user space how to handle new object with wrong id.

2) After a sucessful id allocation attempt, "next_id" will be set back
   to -1 (if it was non-negative).

[akpm@linux-foundation.org: checkpatch fixes]
Signed-off-by: Stanislav Kinsbursky <skinsbursky@parallels.com>
Cc: Serge Hallyn <serge.hallyn@canonical.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Pavel Emelyanov <xemul@parallels.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Michael Kerrisk <mtk.manpages@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Stanislav Kinsbursky 2013-01-04 15:34:50 -08:00 • committed by Linus Torvalds
parent 9afdacda02
commit 03f5956680
5 changed files with 65 additions and 4 deletions
Download patch file Download diff file Expand all files Collapse all files

16
ipc/util.c
View file

@ -122,6 +122,7 @@ void ipc_init_ids(struct ipc_ids *ids)
ids->in_use = 0;
ids->seq = 0;
ids->next_id = -1;
{
int seq_limit = INT_MAX/SEQ_MULTIPLIER;
if (seq_limit > USHRT_MAX)
@ -252,6 +253,7 @@ int ipc_addid(struct ipc_ids* ids, struct kern_ipc_perm* new, int size)
kuid_t euid;
kgid_t egid;
int id, err;
int next_id = ids->next_id;
if (size > IPCMNI)
size = IPCMNI;
@ -264,7 +266,8 @@ int ipc_addid(struct ipc_ids* ids, struct kern_ipc_perm* new, int size)
rcu_read_lock();
spin_lock(&new->lock);
err = idr_get_new(&ids->ipcs_idr, new, &id);
err = idr_get_new_above(&ids->ipcs_idr, new,
(next_id < 0) ? 0 : ipcid_to_idx(next_id), &id);
if (err) {
spin_unlock(&new->lock);
rcu_read_unlock();
@ -277,9 +280,14 @@ int ipc_addid(struct ipc_ids* ids, struct kern_ipc_perm* new, int size)
new->cuid = new->uid = euid;
new->gid = new->cgid = egid;
new->seq = ids->seq++;
if(ids->seq > ids->seq_max)
ids->seq = 0;
if (next_id < 0) {
new->seq = ids->seq++;
if (ids->seq > ids->seq_max)
ids->seq = 0;
} else {
new->seq = ipcid_to_seqx(next_id);
ids->next_id = -1;
}
new->id = ipc_buildid(id, new->seq);
return id;