what the patches do Re: [RFC 10/15] PM / Hibernate: user, implement user_ops reader

Pavel Machek
2010-03-25T05:30:03Z

Hi!

> Switch /dev/snapshot reader to sws_module_ops approach so that we
> can transparently rewrite the rest of the snapshot from pages pulling
> to their pushing through layers.

> struct sws_module_ops user_ops = {
> .storage_available = user_storage_available,
>
> .get_writer = get_user_writer,
> .put_writer = put_user_writer,
> .write_page = user_write_page,
> +
> + .get_reader = get_user_reader,
> + .put_reader = put_user_reader,
> + .read_page = user_read_page,
> };

Ok, I guess that now I see what you are doing.... adding interface
layer between /dev/snapshot and core hibernation code.

To recap, 2.6.33 hibernation looks like:

core hibernation
/\
/ \
swsusp /dev/snapshot
swap \
writing -------- read/write/ioctl interface
\
s2disk

and after your patches, we'd get

core hibernation
/\
---------- sws_module_ops interface
/ \
swsusp /dev/snapshot
swap \
writing -------- read/write/ioctl interface
\
s2disk

(Right? Did I understand the patches correctly?)

I have some problems with sws_module_ops interface (handcoded locking
is too ugly to live), but it is better than I expected. But there may
be better solution available, one that does not need two interfaces to
maintain (we can't really get rid of userland interface). What about
this?

core hibernation
\
\
/dev/snapshot
/ \
---------- read/write/ioctl interface
/ \
swsusp s2disk
swap
writing

? That way, we have just one interface, and still keep the advantages
of modularity / defined interfaces.

(You could literary call sys_read() from inside the kernel -- after
set_fs() -- but going to that extreme is probably not neccessary. But
having interface very similar to what /dev/snapshot provides -- with
the same locking rules -- should result in better code.)

Pavel

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