[PATCH] md: new sysfs interface for setting bits in the write-intent-bitmap

Add a new sysfs interface that allows the bitmap of an array to be dirtied.
The interface is write-only, and is used as follows:

echo "1000" > /sys/block/md2/md/bitmap

(dirty the bit for chunk 1000 [offset 0] in the in-memory and on-disk
bitmaps of array md2)

echo "1000-2000" > /sys/block/md1/md/bitmap

(dirty the bits for chunks 1000-2000 in md1's bitmap)

This is useful, for example, in cluster environments where you may need to
combine two disjoint bitmaps into one (following a server failure, after a
secondary server has taken over the array).  By combining the bitmaps on
the two servers, a full resync can be avoided (This was discussed on the
list back on March 18, 2005, "[PATCH 1/2] md bitmap bug fixes" thread).

Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 31 insertions, 0 deletions

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 8b08043f07ef..b95dd8a183ec 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -2524,6 +2524,36 @@ static struct md_sysfs_entry md_new_device =
 __ATTR(new_dev, S_IWUSR, null_show, new_dev_store);
 
 static ssize_t
+bitmap_store(mddev_t *mddev, const char *buf, size_t len)
+{
+        char *end;
+        unsigned long chunk, end_chunk;
+
+        if (!mddev->bitmap)
+                goto out;
+        /* buf should be <chunk> <chunk> ... or <chunk>-<chunk> ... (range) */
+        while (*buf) {
+                chunk = end_chunk = simple_strtoul(buf, &end, 0);
+                if (buf == end) break;
+                if (*end == '-') { /* range */
+                        buf = end + 1;
+                        end_chunk = simple_strtoul(buf, &end, 0);
+                        if (buf == end) break;
+                }
+                if (*end && !isspace(*end)) break;
+                bitmap_dirty_bits(mddev->bitmap, chunk, end_chunk);
+                buf = end;
+                while (isspace(*buf)) buf++;
+        }
+        bitmap_unplug(mddev->bitmap); /* flush the bits to disk */
+out:
+        return len;
+}
+
+static struct md_sysfs_entry md_bitmap =
+__ATTR(bitmap_set_bits, S_IWUSR, null_show, bitmap_store);
+
+static ssize_t
 size_show(mddev_t *mddev, char *page)
 {
         return sprintf(page, "%llu\n", (unsigned long long)mddev->size);
@@ -2843,6 +2873,7 @@ static struct attribute *md_redundancy_attrs[] = {
         &md_sync_completed.attr,
         &md_suspend_lo.attr,
         &md_suspend_hi.attr,
+        &md_bitmap.attr,
         NULL,
 };
 static struct attribute_group md_redundancy_group = {