On Mon, Mar 22, 2010 at 03:16:35AM -0700, Matt Helsley wrote:
> On Mon, Mar 22, 2010 at 05:34:28PM +1100, Nick Piggin wrote:
> > On Thu, Mar 18, 2010 at 08:59:46PM -0400, Oren Laadan wrote:
> > Hmm, what does generic_file_checkpoint mean? A NULL checkpoint op means
> > that checkpointing is allowed, and no action is required? Shouldn't it
> > be an opt-in operation, where NULL means not allowed?
>
> generic_file_checkpoint is for files that have a seek operation and can be
> backed up or restored with a simple copy.
>
> A NULL checkpoint op means "not allowed" as you thought it should. What
> gave you the impression it was otherwise? Here's the relevant snippet
> from checkpoint/files.c:
Right I didn't check that far. It's just a bit strange to make it look
like filling in an aop function but it is actually still NULL.
>
> /* checkpoint callback for file pointer */
> int checkpoint_file(struct ckpt_ctx *ctx, void *ptr)
> {
> struct file *file = (struct file *) ptr;
> int ret;
>
> if (!file->f_op || !file->f_op->checkpoint) {
> ckpt_err(ctx, -EBADF, "%(T)%(P)%(V)f_op lacks checkpoint\n",
> file, file->f_op);
> return -EBADF;
> }
>
> > Either way, I don't know if you need to have this #define, provided you
> > have sufficient documentation.
>
> We need it (or a suitable replacement) to avoid adding #ifdef around
> assignments to the operation in every filesystem. It's used if
> CONFIG_CHECKPOINT is not defined.
If !CONFIG_CHECKPOINT, ->checkpoint should not exist and neither
should it's callers.
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