linux-kernel - Re: [RFC v4][PATCH 2/9] General infrastructure for checkpoint restart

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Date:	Wed, 10 Sep 2008 14:36:16 -0400
From:	Oren Laadan <orenl@...columbia.edu>
To:	MinChan Kim <minchan.kim@...il.com>
CC:	dave@...ux.vnet.ibm.com, arnd@...db.de, jeremy@...p.org,
	linux-kernel@...r.kernel.org, containers@...ts.linux-foundation.org
Subject: Re: [RFC v4][PATCH 2/9] General infrastructure for checkpoint restart

MinChan Kim wrote:
> On Tue, Sep 9, 2008 at 4:42 PM, Oren Laadan <orenl@...columbia.edu> wrote:

[...]

>> +struct cr_ctx *cr_ctx_alloc(pid_t pid, int fd, unsigned long flags)
>> +{
>> +       struct cr_ctx *ctx;
>> +
>> +       ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
>> +       if (!ctx)
>> +               return ERR_PTR(-ENOMEM);
>> +
>> +       ctx->file = fget(fd);
>> +       if (!ctx->file) {
>> +               cr_ctx_free(ctx);
>> +               return ERR_PTR(-EBADF);
>> +       }
>> +       get_file(ctx->file);
> 
> Why do you need get_file?
> You already called fget.
> Am I missing something ?

This was meant for when we will restart multiple processes, each would
have access to the checkpoint-context, such that the checkpoint-context
may outlives the task that created it and initiated the restart. Thus
the file-pointer will need to stay around longer than that task.

Of course, restart of multiple processes _can_ be coded such that this
first task will always terminate last - either after restart completes
successfully, or after all the other tasks aborted and won't use the
checkpoint-context anymore.

Because that code is not part of the this patch-set, I considered it
safer to grab a reference of the file pointer, making it less likely
that we forget about it later.

> 
>> +       ctx->hbuf = (void *) __get_free_pages(GFP_KERNEL, CR_HBUF_ORDER);
>> +       if (!ctx->hbuf) {
>> +               cr_ctx_free(ctx);
>> +               return ERR_PTR(-ENOMEM);
>> +       }
>> +
>> +       ctx->pid = pid;
>> +       ctx->flags = flags;
>> +
>> +       ctx->crid = atomic_inc_return(&cr_ctx_count);
>> +
>> +       return ctx;
>> +}

Oren.

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