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>

1 files changed, 78 insertions, 62 deletions

diff --git a/mm/swapfile.c b/mm/swapfile.c
index 4dade515b086..5e13bff1764c 100644
--- 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) {