drbd: cleanup ondisk meta data layout calculations and defines

Add a comment about our meta data layout variants,
and rename a few defines (e.g. MD_RESERVED_SECT -> MD_128MB_SECT)
to make it clear that they are short hand for fixed constants,
and not arbitrarily to be redefined as one may see fit.

Properly pad struct meta_data_on_disk to 4kB,
and initialize to zero not only the first 512 Byte,
but all of it in drbd_md_sync().

Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 22 insertions, 6 deletions

diff --git a/drivers/block/drbd/drbd_actlog.c b/drivers/block/drbd/drbd_actlog.c
index 92510f8ad013..b230d91ec430 100644
--- a/drivers/block/drbd/drbd_actlog.c
+++ b/drivers/block/drbd/drbd_actlog.c
@@ -209,7 +209,8 @@ int drbd_md_sync_page_io(struct drbd_conf *mdev, struct drbd_backing_dev *bdev,
                      current->comm, current->pid, __func__,
                      (unsigned long long)sector, (rw & WRITE) ? "WRITE" : "READ");
 
-        err = _drbd_md_sync_page_io(mdev, bdev, iop, sector, rw, MD_BLOCK_SIZE);
+        /* we do all our meta data IO in aligned 4k blocks. */
+        err = _drbd_md_sync_page_io(mdev, bdev, iop, sector, rw, 4096);
         if (err) {
                 dev_err(DEV, "drbd_md_sync_page_io(,%llus,%s) failed with error %d\n",
                     (unsigned long long)sector, (rw & WRITE) ? "WRITE" : "READ", err);
@@ -350,6 +351,24 @@ static unsigned int rs_extent_to_bm_page(unsigned int rs_enr)
                  (BM_EXT_SHIFT - BM_BLOCK_SHIFT));
 }
 
+static sector_t al_tr_number_to_on_disk_sector(struct drbd_conf *mdev)
+{
+        const unsigned int stripes = 1;
+        const unsigned int stripe_size_4kB = MD_32kB_SECT/MD_4kB_SECT;
+
+        /* transaction number, modulo on-disk ring buffer wrap around */
+        unsigned int t = mdev->al_tr_number % (stripe_size_4kB * stripes);
+
+        /* ... to aligned 4k on disk block */
+        t = ((t % stripes) * stripe_size_4kB) + t/stripes;
+
+        /* ... to 512 byte sector in activity log */
+        t *= 8;
+
+        /* ... plus offset to the on disk position */
+        return mdev->ldev->md.md_offset + mdev->ldev->md.al_offset + t;
+}
+
 static int
 _al_write_transaction(struct drbd_conf *mdev)
 {
@@ -432,13 +451,12 @@ _al_write_transaction(struct drbd_conf *mdev)
         if (mdev->al_tr_cycle >= mdev->act_log->nr_elements)
                 mdev->al_tr_cycle = 0;
 
-        sector =  mdev->ldev->md.md_offset
-                + mdev->ldev->md.al_offset
-                + mdev->al_tr_pos * (MD_BLOCK_SIZE>>9);
+        sector = al_tr_number_to_on_disk_sector(mdev);
 
         crc = crc32c(0, buffer, 4096);
         buffer->crc32c = cpu_to_be32(crc);
 
+        /* normal execution path goes through all three branches */
         if (drbd_bm_write_hinted(mdev))
                 err = -EIO;
                 /* drbd_chk_io_error done already */
@@ -446,8 +464,6 @@ _al_write_transaction(struct drbd_conf *mdev)
                 err = -EIO;
                 drbd_chk_io_error(mdev, 1, DRBD_META_IO_ERROR);
         } else {
-                /* advance ringbuffer position and transaction counter */
-                mdev->al_tr_pos = (mdev->al_tr_pos + 1) % (MD_AL_SECTORS*512/MD_BLOCK_SIZE);
                 mdev->al_tr_number++;
         }