Messages in this thread | | | Date | Wed, 4 Apr 2012 16:12:24 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH 2/2] IPC: message queue stealing feature introduced |
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On Wed, 15 Feb 2012 20:54:39 +0400 Stanislav Kinsbursky <skinsbursky@parallels.com> wrote:
> v2: > 1) compat functions added. > 2) message slot size in array is now aligned by struct msgbuf_a. > 3) check for enough free space in buffer before message copying added. > 4) if MSG_STEAL flag is set, then do_msgrcv() returns number of bytes written > to buffer. > 5) flag MSG_NOERROR is ignored if MSG_STEAL flag is set. > > This patch is required for checkpoint/restore in userspace. > IOW, c/r requires some way to get all pending IPC messages without deleting > them for the queue (checkpoint can fail and in this case tasks will be resumed, > so queue have to be valid). > To achive this, new operation flag MSG_STEAL for sys_msgrcv() system call > introduced. > If this flag is set, then passed struct msgbuf pointer will be used for storing > array of structures: > > struct msgbuf_a { > long mtype; /* type of message */ > int msize; /* size of message */ > char mtext[0]; /* message text */ > }; > > each of which will be followed by corresponding message data. >
I'd be a bit more comfortable if there was some sign that other c/r developers have reviewed and tested this and have successfully used it in c/r operation testing?
We've been trying to isolate the c/r-specific functions inside #ifdef CONFIG_CHECKPOINT_RESTORE, but this patch doesn't do that. I have been encouraging this isolation so that people who aren't using c/r don't have to carry the overhead it adds and so that we can more easily hunt down and remove everything if the entire c/r project doesn't work out successfully.
This patch modifies the sys_msgrcv() API and so we should update the manpage for that syscall. Please work with Michael on this.
What does all the compat fiddling actually do? I guess it's needed for checkpoint and restore of 32-bit userspace on 64-bit kernels? Does c/r as a whole support that? It should. How well tested is this?
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