sys_swapon: separate parsing of swapfile header

Move the code which parses and checks the swapfile header (except for
the bad block list) to a separate function. Only code movement, no
functional changes.

Signed-off-by: Cesar Eduardo Barros <cesarb@cesarb.net>
Tested-by: Eric B Munson <emunson@mgebm.net>
Acked-by: Eric B Munson <emunson@mgebm.net>
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/swapfile.c b/mm/swapfile.c
index 4dade51..5e13bff 100644 (file)
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1918,6 +1918,82 @@ static int claim_swapfile(struct swap_info_struct *p, struct inode *inode)
        return 0;
 }
 
+static unsigned long read_swap_header(struct swap_info_struct *p,
+                                       union swap_header *swap_header,
+                                       struct inode *inode)
+{
+       int i;
+       unsigned long maxpages;
+       unsigned long swapfilepages;
+
+       if (memcmp("SWAPSPACE2", swap_header->magic.magic, 10)) {
+               printk(KERN_ERR "Unable to find swap-space signature\n");
+               goto bad_swap;
+       }
+
+       /* swap partition endianess hack... */
+       if (swab32(swap_header->info.version) == 1) {
+               swab32s(&swap_header->info.version);
+               swab32s(&swap_header->info.last_page);
+               swab32s(&swap_header->info.nr_badpages);
+               for (i = 0; i < swap_header->info.nr_badpages; i++)
+                       swab32s(&swap_header->info.badpages[i]);
+       }
+       /* Check the swap header's sub-version */
+       if (swap_header->info.version != 1) {
+               printk(KERN_WARNING
+                      "Unable to handle swap header version %d\n",
+                      swap_header->info.version);
+               goto bad_swap;
+       }
+
+       p->lowest_bit  = 1;
+       p->cluster_next = 1;
+       p->cluster_nr = 0;
+
+       /*
+        * Find out how many pages are allowed for a single swap
+        * device. There are two limiting factors: 1) the number of
+        * bits for the swap offset in the swp_entry_t type and
+        * 2) the number of bits in the a swap pte as defined by
+        * the different architectures. In order to find the
+        * largest possible bit mask a swap entry with swap type 0
+        * and swap offset ~0UL is created, encoded to a swap pte,
+        * decoded to a swp_entry_t again and finally the swap
+        * offset is extracted. This will mask all the bits from
+        * the initial ~0UL mask that can't be encoded in either
+        * the swp_entry_t or the architecture definition of a
+        * swap pte.
+        */
+       maxpages = swp_offset(pte_to_swp_entry(
+                       swp_entry_to_pte(swp_entry(0, ~0UL)))) + 1;
+       if (maxpages > swap_header->info.last_page) {
+               maxpages = swap_header->info.last_page + 1;
+               /* p->max is an unsigned int: don't overflow it */
+               if ((unsigned int)maxpages == 0)
+                       maxpages = UINT_MAX;
+       }
+       p->highest_bit = maxpages - 1;
+
+       if (!maxpages)
+               goto bad_swap;
+       swapfilepages = i_size_read(inode) >> PAGE_SHIFT;
+       if (swapfilepages && maxpages > swapfilepages) {
+               printk(KERN_WARNING
+                      "Swap area shorter than signature indicates\n");
+               goto bad_swap;
+       }
+       if (swap_header->info.nr_badpages && S_ISREG(inode->i_mode))
+               goto bad_swap;
+       if (swap_header->info.nr_badpages > MAX_SWAP_BADPAGES)
+               goto bad_swap;
+
+       return maxpages;
+
+bad_swap:
+       return 0;
+}
+
 SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
 {
        struct swap_info_struct *p;
@@ -1931,7 +2007,6 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
        int nr_extents = 0;
        sector_t span;
        unsigned long maxpages;
-       unsigned long swapfilepages;
        unsigned char *swap_map = NULL;
        struct page *page = NULL;
        struct inode *inode = NULL;
@@ -1989,71 +2064,12 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
        }
        swap_header = kmap(page);
 
-       if (memcmp("SWAPSPACE2", swap_header->magic.magic, 10)) {
-               printk(KERN_ERR "Unable to find swap-space signature\n");
+       maxpages = read_swap_header(p, swap_header, inode);
+       if (unlikely(!maxpages)) {
                error = -EINVAL;
                goto bad_swap;
        }
 
-       /* swap partition endianess hack... */
-       if (swab32(swap_header->info.version) == 1) {
-               swab32s(&swap_header->info.version);
-               swab32s(&swap_header->info.last_page);
-               swab32s(&swap_header->info.nr_badpages);
-               for (i = 0; i < swap_header->info.nr_badpages; i++)
-                       swab32s(&swap_header->info.badpages[i]);
-       }
-       /* Check the swap header's sub-version */
-       if (swap_header->info.version != 1) {
-               printk(KERN_WARNING
-                      "Unable to handle swap header version %d\n",
-                      swap_header->info.version);
-               error = -EINVAL;
-               goto bad_swap;
-       }
-
-       p->lowest_bit  = 1;
-       p->cluster_next = 1;
-       p->cluster_nr = 0;
-
-       /*
-        * Find out how many pages are allowed for a single swap
-        * device. There are two limiting factors: 1) the number of
-        * bits for the swap offset in the swp_entry_t type and
-        * 2) the number of bits in the a swap pte as defined by
-        * the different architectures. In order to find the
-        * largest possible bit mask a swap entry with swap type 0
-        * and swap offset ~0UL is created, encoded to a swap pte,
-        * decoded to a swp_entry_t again and finally the swap
-        * offset is extracted. This will mask all the bits from
-        * the initial ~0UL mask that can't be encoded in either
-        * the swp_entry_t or the architecture definition of a
-        * swap pte.
-        */
-       maxpages = swp_offset(pte_to_swp_entry(
-                       swp_entry_to_pte(swp_entry(0, ~0UL)))) + 1;
-       if (maxpages > swap_header->info.last_page) {
-               maxpages = swap_header->info.last_page + 1;
-               /* p->max is an unsigned int: don't overflow it */
-               if ((unsigned int)maxpages == 0)
-                       maxpages = UINT_MAX;
-       }
-       p->highest_bit = maxpages - 1;
-
-       error = -EINVAL;
-       if (!maxpages)
-               goto bad_swap;
-       swapfilepages = i_size_read(inode) >> PAGE_SHIFT;
-       if (swapfilepages && maxpages > swapfilepages) {
-               printk(KERN_WARNING
-                      "Swap area shorter than signature indicates\n");
-               goto bad_swap;
-       }
-       if (swap_header->info.nr_badpages && S_ISREG(inode->i_mode))
-               goto bad_swap;
-       if (swap_header->info.nr_badpages > MAX_SWAP_BADPAGES)
-               goto bad_swap;
-
        /* OK, set up the swap map and apply the bad block list */
        swap_map = vzalloc(maxpages);
        if (!swap_map) {