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    Subject[PATCH 1/3] bdi: Use parent filesystem BDI for inodes not capable of writeback
    Date
    If inode->i_mapping->backing_dev_info is not capable of writeback
    but the inode gets dirty (because inode itself has changed), use
    inode lists of a bdi of a filesystem holding the device inode.
    Forking the flusher thread just to do the writeout of a single
    inode would be silly and generally bdi needn't be prepared to do
    any writeback.

    This is part of fixing a bug
    https://bugzilla.kernel.org/show_bug.cgi?id=16312.

    Signed-off-by: Jan Kara <jack@suse.cz>
    ---
    fs/fs-writeback.c | 17 +++++++++++++++--
    1 files changed, 15 insertions(+), 2 deletions(-)

    diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
    index d5be169..00865aa 100644
    --- a/fs/fs-writeback.c
    +++ b/fs/fs-writeback.c
    @@ -28,8 +28,6 @@
    #include <linux/buffer_head.h>
    #include "internal.h"

    -#define inode_to_bdi(inode) ((inode)->i_mapping->backing_dev_info)
    -
    /*
    * We don't actually have pdflush, but this one is exported though /proc...
    */
    @@ -50,6 +48,21 @@ struct wb_writeback_work {
    struct completion *done; /* set if the caller waits */
    };

    +static struct backing_dev_info *inode_to_bdi(struct inode *inode)
    +{
    + struct backing_dev_info *bdi = inode->i_mapping->backing_dev_info;
    +
    + /*
    + * This is a hack but it solves a problem with device inode
    + * for e.g. /dev/zero getting dirty (via touch or so) and confusing
    + * writeback code. In such cases we return the "parent" filesystem's
    + * bdi.
    + */
    + if (bdi_cap_writeback_dirty(bdi))
    + return bdi;
    + return inode->i_sb->s_bdi;
    +}
    +
    /**
    * writeback_in_progress - determine whether there is writeback in progress
    * @bdi: the device's backing_dev_info structure.
    --
    1.6.4.2


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