1 files changed, 52 insertions, 0 deletions

diff --git a/fs/buffer.c b/fs/buffer.c
index 3586fb05c8ce..c4e11390a44c 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -2893,6 +2893,55 @@ static void end_bio_bh_io_sync(struct bio *bio, int err)
         bio_put(bio);
 }
 
+/*
+ * This allows us to do IO even on the odd last sectors
+ * of a device, even if the bh block size is some multiple
+ * of the physical sector size.
+ *
+ * We'll just truncate the bio to the size of the device,
+ * and clear the end of the buffer head manually.
+ *
+ * Truly out-of-range accesses will turn into actual IO
+ * errors, this only handles the "we need to be able to
+ * do IO at the final sector" case.
+ */
+static void guard_bh_eod(int rw, struct bio *bio, struct buffer_head *bh)
+{
+        sector_t maxsector;
+        unsigned bytes;
+
+        maxsector = i_size_read(bio->bi_bdev->bd_inode) >> 9;
+        if (!maxsector)
+                return;
+
+        /*
+         * If the *whole* IO is past the end of the device,
+         * let it through, and the IO layer will turn it into
+         * an EIO.
+         */
+        if (unlikely(bio->bi_sector >= maxsector))
+                return;
+
+        maxsector -= bio->bi_sector;
+        bytes = bio->bi_size;
+        if (likely((bytes >> 9) <= maxsector))
+                return;
+
+        /* Uhhuh. We've got a bh that straddles the device size! */
+        bytes = maxsector << 9;
+
+        /* Truncate the bio.. */
+        bio->bi_size = bytes;
+        bio->bi_io_vec[0].bv_len = bytes;
+
+        /* ..and clear the end of the buffer for reads */
+        if (rw & READ) {
+                void *kaddr = kmap_atomic(bh->b_page);
+                memset(kaddr + bh_offset(bh) + bytes, 0, bh->b_size - bytes);
+                kunmap_atomic(kaddr);
+        }
+}
+
 int submit_bh(int rw, struct buffer_head * bh)
 {
         struct bio *bio;
@@ -2929,6 +2978,9 @@ int submit_bh(int rw, struct buffer_head * bh)
         bio->bi_end_io = end_bio_bh_io_sync;
         bio->bi_private = bh;
 
+        /* Take care of bh's that straddle the end of the device */
+        guard_bh_eod(rw, bio, bh);
+
         bio_get(bio);
         submit_bio(rw, bio);