[Bug 4784] New: read-only loop mount should use a read-only losetup

bugzilla at busybox.net bugzilla at busybox.net
Tue Feb 21 09:17:37 UTC 2012


           Summary: read-only loop mount should use a read-only losetup
           Product: Busybox
           Version: 1.19.x
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: enhancement
          Priority: P5
         Component: Other
        AssignedTo: unassigned at busybox.net
        ReportedBy: mk at dee.su
                CC: busybox-cvs at busybox.net
   Estimated Hours: 0.0

util-linux's mount -r uses the equivalent of losetup -r (opening the image with
O_RDONLY). This is convenient when one wants to later remount the (read-write)
filesystem hosting the image read-only. Busybox doesn't do that, so the remount
attempt returns a "busy" error. E.g.:

mkdir z mnt
mount -t tmpfs tmpfs z
truncate -s 10M z/aaa
mkfs.ext2 z/aaa
mount -r -o loop -t ext2 z/aaa mnt
mount -o remount,ro z

A workaround in Busybox is temporarily remounting the image-hosting filesystem
read-only before the loop mount (blockdev --setro /dev/loopX after mounting
does not produce the desired effect).

Incidentally, losetup could support -r option in Busybox, too.

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