Manfred Spraul <manfred@xxxxxxxxxxxxxxxx> writes:
>>>>> On 03/14/2018 08:49 PM, Eric W. Biederman wrote:
>>>>>> To make it possible to keep checkpoint/restore working I have renamed
>>>>>> the sysctls from xxx_next_id to xxx_nextid. That is enough change that
>>>>>> a smart CRIU implementation can see that what is exported has changed,
>>>>>> and act accordingly. New kernels will be able to restore the old id's.
>>>>>>
>>>>>> This code still needs some real world testing to verify my assumptions.
>>>>>> And some work with the CRIU implementations to actually add the code
>>>>>> that deals with the new for of id assignment.
>>>>>>
> It means that all existing checkpoint/restore application will not work with a
> new kernel.
> Everyone must first update the checkpoint/restore application, then update the
> kernel.
>
> Is this acceptable?
There is no nead.
I just reread through how next_id is implementated in ipc/util.c and I
had been reading it wrong. There is no need to change the sysctl.
What criu needs is an interface that specifies the next_id to allocate
both the high and the low bits and that is what this the sysctl
provides.
The implemenation could use a little cleanup so it is easier to
understand something like this perhaps:
diff --git a/ipc/util.c b/ipc/util.c
index 3783b7991cc7..2d4ec6e5b70b 100644
--- a/ipc/util.c
+++ b/ipc/util.c
@@ -192,46 +192,32 @@ static struct kern_ipc_perm *ipc_findkey(struct ipc_ids *ids, key_t key)
return NULL;
}
-#ifdef CONFIG_CHECKPOINT_RESTORE
-/*
- * Specify desired id for next allocated IPC object.
- */
-#define ipc_idr_alloc(ids, new) \
- idr_alloc(&(ids)->ipcs_idr, (new), \
- (ids)->next_id < 0 ? 0 : ipcid_to_idx((ids)->next_id),\
- 0, GFP_NOWAIT)
-
-static inline int ipc_buildid(int id, struct ipc_ids *ids,
- struct kern_ipc_perm *new)
-{
- if (ids->next_id < 0) { /* default, behave as !CHECKPOINT_RESTORE */
- new->seq = ids->seq++;
- if (ids->seq > IPCID_SEQ_MAX)
- ids->seq = 0;
- } else {
- new->seq = ipcid_to_seqx(ids->next_id);
- ids->next_id = -1;
- }
- return SEQ_MULTIPLIER * new->seq + id;
-}
-
-#else
-#define ipc_idr_alloc(ids, new) \
- idr_alloc(&(ids)->ipcs_idr, (new), 0, 0, GFP_NOWAIT)
-
-static inline int ipc_buildid(int id, struct ipc_ids *ids,
- struct kern_ipc_perm *new)
+static inline int ipc_idr_alloc(struct ipc_ids *ids, struct kern_ipc_perm *new)
{
+ int id;
+#ifdef CONFIG_CHECKPOINT_RESTORE
+ if (unlikely(new->id >= 0)) {
+ int idx = ipcid_to_idx(new->id);
+ id = idr_alloc(&ids->ipcs_idr, new, idx, 0, GFP_NOWAIT);
+ if (id < 0)
+ return id;
+ if (id != idx) {
+ idr_remove(&ids->ipcs_idr, id);
+ return -EBUSY;
+ }
+ new->seq = ipcid_to_seqx(new->id);
+ return id;
+ }
+#endif
+ id = idr_alloc(&ids->ipcs_idr, new, 0, 0, GFP_NOWAIT);
new->seq = ids->seq++;
if (ids->seq > IPCID_SEQ_MAX)
ids->seq = 0;
-
- return SEQ_MULTIPLIER * new->seq + id;
+ new->id = SEQ_MULTIPLIER * new->seq + id;
+ return id;
}
-#endif /* CONFIG_CHECKPOINT_RESTORE */
-
/**
* ipc_addid - add an ipc identifier
* @ids: ipc identifier set
@@ -269,6 +255,10 @@ int ipc_addid(struct ipc_ids *ids, struct kern_ipc_perm *new, int limit)
new->cuid = new->uid = euid;
new->gid = new->cgid = egid;
+ new->id = ids->next_id;
+ if (new->id >= 0)
+ ids->next_id = -1;
+
id = ipc_idr_alloc(ids, new);
idr_preload_end();
@@ -290,8 +280,6 @@ int ipc_addid(struct ipc_ids *ids, struct kern_ipc_perm *new, int limit)
if (id > ids->max_id)
ids->max_id = id;
- new->id = ipc_buildid(id, ids, new);
-
return id;
}
Eric
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