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    SubjectRe: [patch|rfc] block: don't mark buffers beyond end of disk as mapped
    Date
    Jeff Moyer <jmoyer@redhat.com> writes:

    > Nick Piggin <npiggin@gmail.com> writes:
    >
    >> On 2 May 2012 00:08, Jeff Moyer <jmoyer@redhat.com> wrote:
    >>> Nick Piggin <npiggin@gmail.com> writes:
    >>>
    >>>> Not a bad fix. But it's kind of sad to have i_size checking logic also in
    >>>> block_read_full_page, that does not cope with this.
    >>>>
    >>>> I have found there are parts of the kernel (readahead) that try to read
    >>>> beyond EOF and seem to get angry if we return an error (by not
    >>>> marking uptodate in readpage) in that case though :(
    >>>>
    >>>> But, either way, I think it's very reasonable to not mark buffers beyond
    >>>> end of device as mapped. So I think your patch is fine.
    >>>>
    >>>> I guess for ext[234], it does not read metadata close to the end of the
    >>>> device or you were using 4K sized blocks?
    >>>
    >>> Well, the test case just reads directly from the loop device, bypassing
    >>> the file system, and I did use 1KB blocks when making the file system, so
    >>> it is quite puzzling.
    >>
    >> It's because buffer_head creation does not go through the same paths
    >> for bdev file access versus getblk APIs.
    >>
    >> blkdev_get_block does the right thing there
    >>
    >> In fact, it's probably good to unify the checks here, i.e., use max_blocks()
    >
    > You really think it's worth it? I mean, it's just an i_size_read and a
    > shift, and there is precedent for it inside fs/buffer.c. I'd prefer to
    > keep the patch as-is, but will change it if you feel that strongly about
    > it.

    Anyway, here is the other version of the patch, using max_block as you
    suggested.

    Cheers,
    Jeff

    Signed-off-by: Jeff Moyer <jmoyer@redhat.com>

    diff --git a/fs/block_dev.c b/fs/block_dev.c
    index e08f6a2..ba11c30 100644
    --- a/fs/block_dev.c
    +++ b/fs/block_dev.c
    @@ -70,7 +70,7 @@ static void bdev_inode_switch_bdi(struct inode *inode,
    spin_unlock(&dst->wb.list_lock);
    }

    -static sector_t max_block(struct block_device *bdev)
    +sector_t blkdev_max_block(struct block_device *bdev)
    {
    sector_t retval = ~((sector_t)0);
    loff_t sz = i_size_read(bdev->bd_inode);
    @@ -163,7 +163,7 @@ static int
    blkdev_get_block(struct inode *inode, sector_t iblock,
    struct buffer_head *bh, int create)
    {
    - if (iblock >= max_block(I_BDEV(inode))) {
    + if (iblock >= blkdev_max_block(I_BDEV(inode))) {
    if (create)
    return -EIO;

    @@ -185,7 +185,7 @@ static int
    blkdev_get_blocks(struct inode *inode, sector_t iblock,
    struct buffer_head *bh, int create)
    {
    - sector_t end_block = max_block(I_BDEV(inode));
    + sector_t end_block = blkdev_max_block(I_BDEV(inode));
    unsigned long max_blocks = bh->b_size >> inode->i_blkbits;

    if ((iblock + max_blocks) > end_block) {
    diff --git a/fs/buffer.c b/fs/buffer.c
    index 351e18e..ad5938c 100644
    --- a/fs/buffer.c
    +++ b/fs/buffer.c
    @@ -921,6 +921,7 @@ init_page_buffers(struct page *page, struct block_device *bdev,
    struct buffer_head *head = page_buffers(page);
    struct buffer_head *bh = head;
    int uptodate = PageUptodate(page);
    + sector_t end_block = blkdev_max_block(I_BDEV(bdev->bd_inode));

    do {
    if (!buffer_mapped(bh)) {
    @@ -929,7 +930,8 @@ init_page_buffers(struct page *page, struct block_device *bdev,
    bh->b_blocknr = block;
    if (uptodate)
    set_buffer_uptodate(bh);
    - set_buffer_mapped(bh);
    + if (block < end_block)
    + set_buffer_mapped(bh);
    }
    block++;
    bh = bh->b_this_page;
    diff --git a/include/linux/fs.h b/include/linux/fs.h
    index 8de6755..25c40b9 100644
    --- a/include/linux/fs.h
    +++ b/include/linux/fs.h
    @@ -2051,6 +2051,7 @@ extern void unregister_blkdev(unsigned int, const char *);
    extern struct block_device *bdget(dev_t);
    extern struct block_device *bdgrab(struct block_device *bdev);
    extern void bd_set_size(struct block_device *, loff_t size);
    +extern sector_t blkdev_max_block(struct block_device *bdev);
    extern void bd_forget(struct inode *inode);
    extern void bdput(struct block_device *);
    extern void invalidate_bdev(struct block_device *);

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      Last update: 2012-05-02 00:21    [W:0.029 / U:0.156 seconds]
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