[PATCH] swsusp: use partition device and offset to identify swap areas

The Linux kernel handles swap files almost in the same way as it handles swap
partitions and there are only two differences between these two types of swap
areas:

(1) swap files need not be contiguous,

(2) the header of a swap file is not in the first block of the partition
    that holds it.  From the swsusp's point of view (1) is not a problem,
    because it is already taken care of by the swap-handling code, but (2) has
    to be taken into consideration.

In principle the location of a swap file's header may be determined with the
help of appropriate filesystem driver.  Unfortunately, however, it requires
the filesystem holding the swap file to be mounted, and if this filesystem is
journaled, it cannot be mounted during a resume from disk.  For this reason we
need some other means by which swap areas can be identified.

For example, to identify a swap area we can use the partition that holds the
area and the offset from the beginning of this partition at which the swap
header is located.

The following patch allows swsusp to identify swap areas this way.  It changes
swap_type_of() so that it takes an additional argument representing an offset
of the swap header within the partition represented by its first argument.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 1 insertions, 1 deletions

diff --git a/include/linux/swap.h b/include/linux/swap.h
index 89f8a39773b..d51e35e4e16 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -247,7 +247,7 @@ extern int swap_duplicate(swp_entry_t);
 extern int valid_swaphandles(swp_entry_t, unsigned long *);
 extern void swap_free(swp_entry_t);
 extern void free_swap_and_cache(swp_entry_t);
-extern int swap_type_of(dev_t);
+extern int swap_type_of(dev_t, sector_t);
 extern unsigned int count_swap_pages(int, int);
 extern sector_t map_swap_page(struct swap_info_struct *, pgoff_t);
 extern struct swap_info_struct *get_swap_info_struct(unsigned);