mm: swap: implement generic handler for swap_activate

The version of swap_activate introduced is sufficient for swap-over-NFS
but would not provide enough information to implement a generic handler.
This patch shuffles things slightly to ensure the same information is
available for aops->swap_activate() as is available to the core.

No functionality change.

Signed-off-by: Mel Gorman <mgorman@suse.de>
Acked-by: Rik van Riel <riel@redhat.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: David S. Miller <davem@davemloft.net>
Cc: Eric B Munson <emunson@mgebm.net>
Cc: Eric Paris <eparis@redhat.com>
Cc: James Morris <jmorris@namei.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Mike Christie <michaelc@cs.wisc.edu>
Cc: Neil Brown <neilb@suse.de>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>
Cc: Trond Myklebust <Trond.Myklebust@netapp.com>
Cc: Xiaotian Feng <dfeng@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 92 insertions, 0 deletions

diff --git a/mm/page_io.c b/mm/page_io.c
index 307a3e795290..4a379629e31f 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -87,6 +87,98 @@ void end_swap_bio_read(struct bio *bio, int err)
         bio_put(bio);
 }
 
+int generic_swapfile_activate(struct swap_info_struct *sis,
+                                struct file *swap_file,
+                                sector_t *span)
+{
+        struct address_space *mapping = swap_file->f_mapping;
+        struct inode *inode = mapping->host;
+        unsigned blocks_per_page;
+        unsigned long page_no;
+        unsigned blkbits;
+        sector_t probe_block;
+        sector_t last_block;
+        sector_t lowest_block = -1;
+        sector_t highest_block = 0;
+        int nr_extents = 0;
+        int ret;
+
+        blkbits = inode->i_blkbits;
+        blocks_per_page = PAGE_SIZE >> blkbits;
+
+        /*
+         * Map all the blocks into the extent list.  This code doesn't try
+         * to be very smart.
+         */
+        probe_block = 0;
+        page_no = 0;
+        last_block = i_size_read(inode) >> blkbits;
+        while ((probe_block + blocks_per_page) <= last_block &&
+                        page_no < sis->max) {
+                unsigned block_in_page;
+                sector_t first_block;
+
+                first_block = bmap(inode, probe_block);
+                if (first_block == 0)
+                        goto bad_bmap;
+
+                /*
+                 * It must be PAGE_SIZE aligned on-disk
+                 */
+                if (first_block & (blocks_per_page - 1)) {
+                        probe_block++;
+                        goto reprobe;
+                }
+
+                for (block_in_page = 1; block_in_page < blocks_per_page;
+                                        block_in_page++) {
+                        sector_t block;
+
+                        block = bmap(inode, probe_block + block_in_page);
+                        if (block == 0)
+                                goto bad_bmap;
+                        if (block != first_block + block_in_page) {
+                                /* Discontiguity */
+                                probe_block++;
+                                goto reprobe;
+                        }
+                }
+
+                first_block >>= (PAGE_SHIFT - blkbits);
+                if (page_no) {  /* exclude the header page */
+                        if (first_block < lowest_block)
+                                lowest_block = first_block;
+                        if (first_block > highest_block)
+                                highest_block = first_block;
+                }
+
+                /*
+                 * We found a PAGE_SIZE-length, PAGE_SIZE-aligned run of blocks
+                 */
+                ret = add_swap_extent(sis, page_no, 1, first_block);
+                if (ret < 0)
+                        goto out;
+                nr_extents += ret;
+                page_no++;
+                probe_block += blocks_per_page;
+reprobe:
+                continue;
+        }
+        ret = nr_extents;
+        *span = 1 + highest_block - lowest_block;
+        if (page_no == 0)
+                page_no = 1;    /* force Empty message */
+        sis->max = page_no;
+        sis->pages = page_no - 1;
+        sis->highest_bit = page_no - 1;
+out:
+        return ret;
+bad_bmap:
+        printk(KERN_ERR "swapon: swapfile has holes\n");
+        ret = -EINVAL;
+        goto out;
+}
+
 /*
  * We may have stale swap cache pages in memory: notice
  * them here and get rid of the unnecessary final write.