Messages in this thread | | | Date | Wed, 30 Jan 2008 00:06:56 +0300 | Subject | Re: [PATCH 2.6.24-rc8-mm1 09/15] (RFC) IPC: new kernel API to change an ID | From | Alexey Dobriyan <> |
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On Tue, Jan 29, 2008 at 05:02:38PM +0100, pierre.peiffer@bull.net wrote: > This patch provides three new API to change the ID of an existing > System V IPCs. > > These APIs are: > long msg_chid(struct ipc_namespace *ns, int id, int newid); > long sem_chid(struct ipc_namespace *ns, int id, int newid); > long shm_chid(struct ipc_namespace *ns, int id, int newid); > > They return 0 or an error code in case of failure. > > They may be useful for setting a specific ID for an IPC when preparing > a restart operation. > > To be successful, the following rules must be respected: > - the IPC exists (of course...) > - the new ID must satisfy the ID computation rule. > - the entry in the idr corresponding to the new ID must be free.
> ipc/util.c | 48 ++++++++++++++++++++++++++++++++++++++++++++++++ > ipc/util.h | 1 + > 8 files changed, 197 insertions(+)
For the record, OpenVZ uses "create with predefined ID" method which leads to less code. For example, change at the end is all we want from ipc/util.c .
Also, if ids were A and B at the moment of checkpoint, and during restart they became B and A you'll get collision in both ways which you techically can avoid by classic "tmp = A, A = B, B = tmp" but you also can avoid all other loops just by creating with ID you need.
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