On Mon, Jun 20, 2016 at 02:35:29PM +0200, Bart Van Assche wrote:
> On 06/17/2016 03:18 AM, Darrick J. Wong wrote:
> >Invalidate the page cache (as a regular O_DIRECT write would do) to avoid
> >returning stale cache contents at a later time.
> >
> >v5: Refactor the 4.4 refactoring of the ioctl code into separate functions.
> >Split the page invalidation and the new ioctl into separate patches.
> >
> >Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
> >Reviewed-by: Christoph Hellwig <hch@xxxxxx>
> >---
> > block/ioctl.c | 29 +++++++++++++++++++++++------
> > 1 file changed, 23 insertions(+), 6 deletions(-)
> >
> >
> >diff --git a/block/ioctl.c b/block/ioctl.c
> >index ed2397f..d001f52 100644
> >--- a/block/ioctl.c
> >+++ b/block/ioctl.c
> >@@ -225,7 +225,9 @@ static int blk_ioctl_zeroout(struct block_device *bdev, fmode_t mode,
> > unsigned long arg)
> > {
> > uint64_t range[2];
> >- uint64_t start, len;
> >+ struct address_space *mapping;
> >+ uint64_t start, end, len;
> >+ int ret;
> >
> > if (!(mode & FMODE_WRITE))
> > return -EBADF;
> >@@ -235,18 +237,33 @@ static int blk_ioctl_zeroout(struct block_device *bdev, fmode_t mode,
> >
> > start = range[0];
> > len = range[1];
> >+ end = start + len - 1;
> >
> > if (start & 511)
> > return -EINVAL;
> > if (len & 511)
> > return -EINVAL;
> >- start >>= 9;
> >- len >>= 9;
> >-
> >- if (start + len > (i_size_read(bdev->bd_inode) >> 9))
> >+ if (end >= (uint64_t)i_size_read(bdev->bd_inode))
> >+ return -EINVAL;
> >+ if (end < start)
> > return -EINVAL;
> >
> >- return blkdev_issue_zeroout(bdev, start, len, GFP_KERNEL, false);
> >+ /* Invalidate the page cache, including dirty pages */
> >+ mapping = bdev->bd_inode->i_mapping;
> >+ truncate_inode_pages_range(mapping, start, end);
> >+
> >+ ret = blkdev_issue_zeroout(bdev, start >> 9, len >> 9, GFP_KERNEL,
> >+ false);
> >+ if (ret)
> >+ return ret;
> >+
> >+ /*
> >+ * Invalidate again; if someone wandered in and dirtied a page,
> >+ * the caller will be given -EBUSY.
> >+ */
> >+ return invalidate_inode_pages2_range(mapping,
> >+ start >> PAGE_SHIFT,
> >+ end >> PAGE_SHIFT);
> > }
>
> Hello Darrick,
>
> Maybe this has already been discussed, but anyway: in the POSIX spec
> (http://pubs.opengroup.org/onlinepubs/9699919799/functions/write.html) I
> found the following: "This volume of POSIX.1-2008 does not specify behavior
> of concurrent writes to a file from multiple processes. Applications should
> use some form of concurrency control."
>
> Do we really need the invalidate_inode_pages2_range() call?
It's not strictly necessary. I like the idea of having the kernel bonking
userspace when they don't coordinate and collide, but we could just jump
out after the blkdev_*() calls and let userspace fend for themselves. :)
--D
>
> Thanks,
>
> Bart.
>
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