Btrfs: check for duplicate iov_base's when doing dio reads (93a54bc4) · Commits · 戴 / test

Apparently it is ok to submit a read to an IDE device with the same target page for different offsets. This is what Windows does under qemu. The problem is under DIO we expect them to be different buffers for checksumming reasons, and so this sort of thing will result in checksum errors, when in reality the file is fine. So when reading, check to make sure that all iov bases are different, and if they aren't fall back to buffered mode, since that will work out right. Thanks, Signed-off-by:

Josef Bacik <josef@redhat.com>

fs/btrfs/inode.c

+16 −1

Original line number	Diff line number	Diff line
		@@ -6207,6 +6207,7 @@ static ssize_t check_direct_IO(struct btrfs_root root, int rw, struct kiocb io
		unsigned long nr_segs)
		{
		int seg;
		int i;
		size_t size;
		unsigned long addr;
		unsigned blocksize_mask = root->sectorsize - 1;
		@@ -6223,6 +6224,20 @@ static ssize_t check_direct_IO(struct btrfs_root root, int rw, struct kiocb io
		end += size;
		if ((addr & blocksize_mask) \|\| (size & blocksize_mask))
		goto out;

		/* If this is a write we don't need to check anymore */
		if (rw & WRITE)
		continue;

		/*
		* Check to make sure we don't have duplicate iov_base's in this
		* iovec, if so return EINVAL, otherwise we'll get csum errors
		* when reading back.
		*/
		for (i = seg + 1; i < nr_segs; i++) {
		if (iov[seg].iov_base == iov[i].iov_base)
		goto out;
		}
		}
		retval = 0;
		out:

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