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    Subject[PATCH 3/9] Unionfs: support lower filesystems without writeback capability
    Date
    Implement unionfs_writepages.  As per
    mm/filemap.c:__filemap_fdatawrite_range(), don't call our writepage if the
    lower mapping has BDI_CAP_NO_WRITEBACK capability set.

    Signed-off-by: Pekka J Enberg <penberg@cs.helsinki.fi>
    Signed-off-by: Erez Zadok <ezk@cs.sunysb.edu>
    ---
    fs/unionfs/mmap.c | 23 +++++++++++++++++++++++
    fs/unionfs/union.h | 1 +
    2 files changed, 24 insertions(+), 0 deletions(-)

    diff --git a/fs/unionfs/mmap.c b/fs/unionfs/mmap.c
    index 6440282..b43557e 100644
    --- a/fs/unionfs/mmap.c
    +++ b/fs/unionfs/mmap.c
    @@ -144,6 +144,28 @@ out:
    return err;
    }

    +static int unionfs_writepages(struct address_space *mapping,
    + struct writeback_control *wbc)
    +{
    + int err = 0;
    + struct inode *lower_inode;
    + struct inode *inode;
    +
    + inode = mapping->host;
    + lower_inode = unionfs_lower_inode(inode);
    + BUG_ON(!lower_inode);
    +
    + if (!mapping_cap_writeback_dirty(lower_inode->i_mapping))
    + goto out;
    +
    + /* Note: generic_writepages may return AOP_WRITEPAGE_ACTIVATE */
    + err = generic_writepages(mapping, wbc);
    + if (err == 0)
    + unionfs_copy_attr_times(inode);
    +out:
    + return err;
    +}
    +
    /*
    * readpage is called from generic_page_read and the fault handler.
    * If your file system uses generic_page_read for the read op, it
    @@ -374,6 +396,7 @@ out:

    struct address_space_operations unionfs_aops = {
    .writepage = unionfs_writepage,
    + .writepages = unionfs_writepages,
    .readpage = unionfs_readpage,
    .prepare_write = unionfs_prepare_write,
    .commit_write = unionfs_commit_write,
    diff --git a/fs/unionfs/union.h b/fs/unionfs/union.h
    index 8eb2ee4..6333488 100644
    --- a/fs/unionfs/union.h
    +++ b/fs/unionfs/union.h
    @@ -45,6 +45,7 @@
    #include <linux/log2.h>
    #include <linux/poison.h>
    #include <linux/mman.h>
    +#include <linux/backing-dev.h>

    #include <asm/system.h>

    --
    1.5.2.2
    -
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