• Paolo Bonzini's avatar
    nbd: fsync and kill block device on shutdown · 3a2d63f8
    Paolo Bonzini authored
    There are two problems with shutdown in the NBD driver.
    
    1: Receiving the NBD_DISCONNECT ioctl does not sync the filesystem.
    
       This patch adds the sync operation into __nbd_ioctl()'s
       NBD_DISCONNECT handler.  This is useful because BLKFLSBUF is restricted
       to processes that have CAP_SYS_ADMIN, and the NBD client may not
       possess it (fsync of the block device does not sync the filesystem,
       either).
    
    2: Once we clear the socket we have no guarantee that later reads will
       come from the same backing storage.
    
       The patch adds calls to kill_bdev() in __nbd_ioctl()'s socket
       clearing code so the page cache is cleaned, lest reads that hit on the
       page cache will return stale data from the previously-accessible disk.
    
    Example:
    
        # qemu-nbd -r -c/dev/nbd0 /dev/sr0
        # file -s /dev/nbd0
        /dev/stdin: # UDF filesystem data (version 1.5) etc.
        # qemu-nbd -d /dev/nbd0
        # qemu-nbd -r -c/dev/nbd0 /dev/sda
        # file -s /dev/nbd0
        /dev/stdin: # UDF filesystem data (version 1.5) etc.
    
    While /dev/sda has:
    
        # file -s /dev/sda
        /dev/sda: x86 boot sector; etc.
    Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
    Acked-by: default avatarPaul Clements <Paul.Clements@steeleye.com>
    Cc: Alex Bligh <alex@alex.org.uk>
    Cc: <stable@vger.kernel.org>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    3a2d63f8
nbd.c 22.2 KB