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    SubjectRe: [PATCH v2] fs: Invalidate the cache for a parent block-device if fsync() is called for a partition
    On 01/23/2012 04:27 PM, Jeff Moyer wrote:
    > Niels de Vos <ndevos@redhat.com> writes:
    >
    >> Executing an fsync() on a file-descriptor of a partition flushes the
    >> caches for that partition by calling blkdev_issue_flush(). However, it
    >> seems that reading data through the parent device will still return the
    >> old cached data.
    >
    > What problem, exactly, are you trying to fix? Could you please post a
    > reproducer?

    The problem that was noticed is the following:
    1) create two or more partitions on a device
    - use fdisk to create /dev/sdb1 and /dev/sdb2
    2) format and mount one of the partition
    - mkfs -t ext3 /dev/sdb1
    3) read through the main device to have something in the cache
    - read /dev/sdb with dd or use something like "parted /dev/sdb print"
    4) now write something to /dev/sdb2, format the partition for example
    - mkfs -t ext3 /dev/sdb2
    5) read the blocks where sdb2 starts, through /dev/sdb
    - use dd or do again a "parted /dev/sdb print"

    Without this patch, calling "blockdev --flushbufs" or dropping the
    caches, the result in 5) is the same as in 3). Reading the same area
    through /dev/sdb2 shows the inconsistancy between the two caches.

    With this patch, or one of the workarounds, the data read through
    /dev/sdb and /dev/sdb2 is the same.

    I hope this explains is clear enough, if not, please let me know.

    Thanks,
    Niels


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