mount: retry on ENOMEDIUM

Due to a change in kernel behaviour when opening CDROM devices,
we need to retry the open/mount call when ENOMEDIUM is returned.

Explanation from Tejun Heo:
Okay, the difference is from the addition of cdrom_get_media_event()
call to both sr_drive_status() and ide_cdrom_drive_status().
Previously, the cdrom driver can't differentiate between tray closed
w/ no media and tray open and always returned tray open, which
triggers close and retry in the open logic which probably have delayed
things enough to get the media recognized.

Now the cdrom driver can discern between tray closed w/o media and
device not ready for other reasons and returns -ENOMEDIUM on the
former.  This is all good and dandy but the problem seems that some
drives report no media right after the tray is closed but it hasn't
properly detected the media yet.

It seems the only way to work around the problem is via sensible
retries (e.g.  try three times 5 secs apart) and I don't think we can
add that type of retry logic into cdrom open path.  Please note that
the previous logic wasn't water proof.  Some drives can take longer to
recognize the media is there and could have failed the in-kernel retry
too.  Also, reading the media can take quite some time and during that
period the drive reports media present but device not ready.  The
driver will retry the command (e.g. READ TOC for open) five times but
all of them can fail w/ EMEDIUMTYPE.

[kzak@redhat.com: - add CRDOM_NOMEDIUM_RETRIES to blkdev.h
                  - add verbose message to mount.c]

Signed-off-by: Matthias Koenig <mkoenig@suse.de>
Signed-off-by: Karel Zak <kzak@redhat.com>

diff --git a/include/blkdev.h b/include/blkdev.h
index 1b10569b9d338978b7ef5fe6099b1351b3b56c79..409b5e43c5d99473ab50fd9cd22cec9726cc932e 100644 (file)
--- a/include/blkdev.h
+++ b/include/blkdev.h
@@ -6,6 +6,9 @@
 
 #define DEFAULT_SECTOR_SIZE       512
 
+/* open() retries when errno is ENOMEDIUM */
+#define CRDOM_NOMEDIUM_RETRIES    5
+
 #if !defined(BLKROSET) && defined(__linux__)
 
 #define BLKROSET   _IO(0x12,93)        /* set device read-only (0 = read-write) */

diff --git a/mount/fsprobe_volumeid.c b/mount/fsprobe_volumeid.c
index 7c98dc6e71326b83f6882e83c1b926ad68cc77f1..949db8298e0308d2ac35e030b5e216f638a41786 100644 (file)
--- a/mount/fsprobe_volumeid.c
+++ b/mount/fsprobe_volumeid.c
@@ -3,6 +3,7 @@
 #include <unistd.h>
 #include <string.h>
 #include <stddef.h>
+#include <errno.h>
 #include <sys/mount.h>
 #include <sys/ioctl.h>
 #include <fcntl.h>
@@ -30,10 +31,18 @@ static char
        struct volume_id *id;
        const char *val;
        char *value = NULL;
+       int retries = 0;
 
+retry:
        fd = open(device, O_RDONLY);
-       if (fd < 0)
+       if (fd < 0) {
+               if (errno == ENOMEDIUM && retries < CRDOM_NOMEDIUM_RETRIES) {
+                       ++retries;
+                       sleep(3);
+                       goto retry;
+               }
                return NULL;
+       }
 
        id = volume_id_open_fd(fd);
        if (!id) {

diff --git a/mount/mount.c b/mount/mount.c
index 39a9bd8589bb408f326ac0bd27a511307f5fa5d7..be051355b9091503c18ebbe12a24a6e11ebdf63c 100644 (file)
--- a/mount/mount.c
+++ b/mount/mount.c
@@ -1071,6 +1071,7 @@ try_mount_one (const char *spec0, const char *node0, const char *types0,
   int loop = 0;
   const char *loopdev = 0, *loopfile = 0;
   struct stat statbuf;
+  int retries = 0;     /* Nr of retries for mount in case of ENOMEDIUM */
 
   /* copies for freeing on exit */
   const char *opts1, *spec1, *node1, *types1, *extra_opts1;
@@ -1133,6 +1134,7 @@ try_mount_one (const char *spec0, const char *node0, const char *types0,
       goto out;
   }
 
+mount_retry:
   block_signals (SIG_BLOCK);
 
   if (!fake) {
@@ -1362,6 +1364,17 @@ try_mount_one (const char *spec0, const char *node0, const char *types0,
       }
       break;
     }
+    case ENOMEDIUM:
+      if (retries < CRDOM_NOMEDIUM_RETRIES) {
+             if (verbose)
+                     printf(_("mount: no medium found on %s ...trying again\n"),
+                                spec);
+              sleep(3);
+             ++retries;
+              goto mount_retry;
+      }
+      error(_("mount: no medium found on %s"), spec);
+      break;
     default:
       error ("mount: %s", strerror (mnt_err)); break;
     }