swapon: rewrite SWSUSPEND signature rather than exec mkswap

> On Thu, Jan 22, 2009 at 04:46:57PM +0000, Hugh Dickins wrote:
> Though your swapon may mkswap for suspend reasons: hmm, wouldn't it
> do very much better just to rewrite the swap signature, than exec
> mkswap - maybe nobody ever uses the badpages list, but it really
> should be respected.

CC: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Karel Zak <kzak@redhat.com>

diff --git a/mount/swapon.c b/mount/swapon.c
index 1c337c266ffe1c9fb4946d3ca7d08a4121ff270a..d61ff74378fc9378469a1126ede4c59a091cbbc6 100644 (file)
--- a/mount/swapon.c
+++ b/mount/swapon.c
@@ -48,6 +48,9 @@ enum {
        SIG_SWSUSPEND
 };
 
+#define SWAP_SIGNATURE         "SWAPSPACE2"
+#define SWAP_SIGNATURE_SZ      (sizeof(SWAP_SIGNATURE) - 1)
+
 int all;
 int priority = -1;     /* non-prioritized swap by default */
 
@@ -228,6 +231,30 @@ swap_reinitialize(const char *device) {
        return -1; /* error */
 }
 
+static int
+swap_rewrite_signature(const char *devname, unsigned int pagesize)
+{
+       int fd, rc = -1;
+
+       fd = open(devname, O_WRONLY);
+       if (fd == -1) {
+               warn(_("%s: open failed"), devname);
+               return -1;
+       }
+
+       if (lseek(fd, pagesize - SWAP_SIGNATURE_SZ, SEEK_SET) < 0)
+               goto err;
+
+       if (write(fd, (void *) SWAP_SIGNATURE,
+                       SWAP_SIGNATURE_SZ) != SWAP_SIGNATURE_SZ)
+               goto err;
+
+       rc  = 0;
+err:
+       close(fd);
+       return rc;
+}
+
 static int
 swap_detect_signature(const char *buf, int *sig)
 {
@@ -271,9 +298,9 @@ swap_get_header(int fd, int *sig, unsigned int *pagesize)
                        continue;
                /* the smallest swap area is PAGE_SIZE*10, it means
                 * 40k, that's less than MAX_PAGESIZE */
-               if (datasz < (page - 10))
+               if (datasz < (page - SWAP_SIGNATURE_SZ))
                        break;
-               if (swap_detect_signature(buf + page - 10, sig)) {
+               if (swap_detect_signature(buf + page - SWAP_SIGNATURE_SZ, sig)) {
                        *pagesize = page;
                        break;
                }
@@ -318,7 +345,6 @@ swap_get_size(const char *hdr, const char *devname, unsigned int pagesize)
 static int
 swapon_checks(const char *special)
 {
-       int reinitialize = 0;
        struct stat st;
        int fd = -1, sig;
        char *hdr = NULL;
@@ -384,7 +410,8 @@ swapon_checks(const char *special)
                        warn(_("%s: swap format pagesize does not match."
                                " Reinitializing the swap."),
                                special);
-                       reinitialize = 1;
+                       if (swap_reinitialize(special) < 0)
+                               goto err;
                }
        } else if (sig == SIG_SWSUSPEND) {
                /* We have to reinitialize swap with old (=useless) software suspend
@@ -392,20 +419,15 @@ swapon_checks(const char *special)
                 * corruption the next time an attempt at unsuspending is made.
                 */
                warnx(_("%s: software suspend data detected. "
-                               "Reinitializing the swap."),
+                               "Rewriting the swap signature."),
                        special);
-               reinitialize = 1;
-       }
-
-       if (reinitialize) {
-               if (swap_reinitialize(special) < 0)
+               if (swap_rewrite_signature(special, pagesize) < 0)
                        goto err;
        }
 
        free(hdr);
        close(fd);
        return 0;
-
 err:
        if (fd != -1)
                close(fd);