md: Support write-intent bitmaps with externally managed metadata.

In this case, the metadata needs to not be in the same
sector as the bitmap.
md will not read/write any bitmap metadata.  Config must be
done via sysfs and when a recovery makes the array non-degraded
again, writing 'true' to 'bitmap/can_clear' will allow bits in
the bitmap to be cleared again.

Signed-off-by: NeilBrown <neilb@suse.de>

4 files changed, 137 insertions, 33 deletions

diff --git a/Documentation/md.txt b/Documentation/md.txt
index 18fad6876228..21d26fb5d02b 100644
--- a/Documentation/md.txt
+++ b/Documentation/md.txt
@@ -322,6 +322,22 @@ All md devices contain:
      'backlog' sets a limit on the number of concurrent background
      writes.  If there are more than this, new writes will by
      synchronous.
+  bitmap/metadata
+     This can be either 'internal' or 'external'.
+     'internal' is the default and means the metadata for the bitmap
+     is stored in the first 256 bytes of the allocated space and is
+     managed by the md module.
+     'external' means that bitmap metadata is managed externally to
+     the kernel (i.e. by some userspace program)
+  bitmap/can_clear
+     This is either 'true' or 'false'.  If 'true', then bits in the
+     bitmap will be cleared when the corresponding blocks are thought
+     to be in-sync.  If 'false', bits will never be cleared.
+     This is automatically set to 'false' if a write happens on a
+     degraded array, or if the array becomes degraded during a write.
+     When metadata is managed externally, it should be set to true
+     once the array becomes non-degraded, and this fact has been
+     recorded in the metadata.
      
      
      
diff --git a/drivers/md/bitmap.c b/drivers/md/bitmap.c
index 62958491f329..de5c42df8d17 100644
--- a/drivers/md/bitmap.c
+++ b/drivers/md/bitmap.c
@@ -497,6 +497,8 @@ void bitmap_update_sb(struct bitmap *bitmap)
 
         if (!bitmap || !bitmap->mddev) /* no bitmap for this array */
                 return;
+        if (bitmap->mddev->bitmap_info.external)
+                return;
         spin_lock_irqsave(&bitmap->lock, flags);
         if (!bitmap->sb_page) { /* no superblock */
                 spin_unlock_irqrestore(&bitmap->lock, flags);
@@ -676,16 +678,26 @@ static int bitmap_mask_state(struct bitmap *bitmap, enum bitmap_state bits,
  * general bitmap file operations
  */
 
+/*
+ * on-disk bitmap:
+ *
+ * Use one bit per "chunk" (block set). We do the disk I/O on the bitmap
+ * file a page at a time. There's a superblock at the start of the file.
+ */
 /* calculate the index of the page that contains this bit */
-static inline unsigned long file_page_index(unsigned long chunk)
+static inline unsigned long file_page_index(struct bitmap *bitmap, unsigned long chunk)
 {
-        return CHUNK_BIT_OFFSET(chunk) >> PAGE_BIT_SHIFT;
+        if (!bitmap->mddev->bitmap_info.external)
+                chunk += sizeof(bitmap_super_t) << 3;
+        return chunk >> PAGE_BIT_SHIFT;
 }
 
 /* calculate the (bit) offset of this bit within a page */
-static inline unsigned long file_page_offset(unsigned long chunk)
+static inline unsigned long file_page_offset(struct bitmap *bitmap, unsigned long chunk)
 {
-        return CHUNK_BIT_OFFSET(chunk) & (PAGE_BITS - 1);
+        if (!bitmap->mddev->bitmap_info.external)
+                chunk += sizeof(bitmap_super_t) << 3;
+        return chunk & (PAGE_BITS - 1);
 }
 
 /*
@@ -698,8 +710,9 @@ static inline unsigned long file_page_offset(unsigned long chunk)
 static inline struct page *filemap_get_page(struct bitmap *bitmap,
                                         unsigned long chunk)
 {
-        if (file_page_index(chunk) >= bitmap->file_pages) return NULL;
-        return bitmap->filemap[file_page_index(chunk) - file_page_index(0)];
+        if (file_page_index(bitmap, chunk) >= bitmap->file_pages) return NULL;
+        return bitmap->filemap[file_page_index(bitmap, chunk)
+                               - file_page_index(bitmap, 0)];
 }
 
 
@@ -722,7 +735,7 @@ static void bitmap_file_unmap(struct bitmap *bitmap)
         spin_unlock_irqrestore(&bitmap->lock, flags);
 
         while (pages--)
-                if (map[pages]->index != 0) /* 0 is sb_page, release it below */
+                if (map[pages] != sb_page) /* 0 is sb_page, release it below */
                         free_buffers(map[pages]);
         kfree(map);
         kfree(attr);
@@ -833,7 +846,7 @@ static void bitmap_file_set_bit(struct bitmap *bitmap, sector_t block)
 
         page = filemap_get_page(bitmap, chunk);
         if (!page) return;
-        bit = file_page_offset(chunk);
+        bit = file_page_offset(bitmap, chunk);
 
         /* set the bit */
         kaddr = kmap_atomic(page, KM_USER0);
@@ -931,14 +944,17 @@ static int bitmap_init_from_disk(struct bitmap *bitmap, sector_t start)
                         "recovery\n", bmname(bitmap));
 
         bytes = (chunks + 7) / 8;
+        if (!bitmap->mddev->bitmap_info.external)
+                bytes += sizeof(bitmap_super_t);
 
-        num_pages = (bytes + sizeof(bitmap_super_t) + PAGE_SIZE - 1) / PAGE_SIZE;
+        
+        num_pages = (bytes + PAGE_SIZE - 1) / PAGE_SIZE;
 
-        if (file && i_size_read(file->f_mapping->host) < bytes + sizeof(bitmap_super_t)) {
+        if (file && i_size_read(file->f_mapping->host) < bytes) {
                 printk(KERN_INFO "%s: bitmap file too short %lu < %lu\n",
                         bmname(bitmap),
                         (unsigned long) i_size_read(file->f_mapping->host),
-                        bytes + sizeof(bitmap_super_t));
+                        bytes);
                 goto err;
         }
 
@@ -959,17 +975,16 @@ static int bitmap_init_from_disk(struct bitmap *bitmap, sector_t start)
 
         for (i = 0; i < chunks; i++) {
                 int b;
-                index = file_page_index(i);
-                bit = file_page_offset(i);
+                index = file_page_index(bitmap, i);
+                bit = file_page_offset(bitmap, i);
                 if (index != oldindex) { /* this is a new page, read it in */
                         int count;
                         /* unmap the old page, we're done with it */
                         if (index == num_pages-1)
-                                count = bytes + sizeof(bitmap_super_t)
-                                        - index * PAGE_SIZE;
+                                count = bytes - index * PAGE_SIZE;
                         else
                                 count = PAGE_SIZE;
-                        if (index == 0) {
+                        if (index == 0 && bitmap->sb_page) {
                                 /*
                                  * if we're here then the superblock page
                                  * contains some bits (PAGE_SIZE != sizeof sb)
@@ -1164,7 +1179,8 @@ void bitmap_daemon_work(mddev_t *mddev)
                         /* We are possibly going to clear some bits, so make
                          * sure that events_cleared is up-to-date.
                          */
-                        if (bitmap->need_sync) {
+                        if (bitmap->need_sync &&
+                            bitmap->mddev->bitmap_info.external == 0) {
                                 bitmap_super_t *sb;
                                 bitmap->need_sync = 0;
                                 sb = kmap_atomic(bitmap->sb_page, KM_USER0);
@@ -1174,7 +1190,8 @@ void bitmap_daemon_work(mddev_t *mddev)
                                 write_page(bitmap, bitmap->sb_page, 1);
                         }
                         spin_lock_irqsave(&bitmap->lock, flags);
-                        clear_page_attr(bitmap, page, BITMAP_PAGE_CLEAN);
+                        if (!bitmap->need_sync)
+                                clear_page_attr(bitmap, page, BITMAP_PAGE_CLEAN);
                 }
                 bmc = bitmap_get_counter(bitmap,
                                          (sector_t)j << CHUNK_BLOCK_SHIFT(bitmap),
@@ -1189,7 +1206,7 @@ void bitmap_daemon_work(mddev_t *mddev)
                         if (*bmc == 2) {
                                 *bmc=1; /* maybe clear the bit next time */
                                 set_page_attr(bitmap, page, BITMAP_PAGE_CLEAN);
-                        } else if (*bmc == 1) {
+                        } else if (*bmc == 1 && !bitmap->need_sync) {
                                 /* we can clear the bit */
                                 *bmc = 0;
                                 bitmap_count_page(bitmap,
@@ -1199,9 +1216,11 @@ void bitmap_daemon_work(mddev_t *mddev)
                                 /* clear the bit */
                                 paddr = kmap_atomic(page, KM_USER0);
                                 if (bitmap->flags & BITMAP_HOSTENDIAN)
-                                        clear_bit(file_page_offset(j), paddr);
+                                        clear_bit(file_page_offset(bitmap, j),
+                                                  paddr);
                                 else
-                                        ext2_clear_bit(file_page_offset(j), paddr);
+                                        ext2_clear_bit(file_page_offset(bitmap, j),
+                                                       paddr);
                                 kunmap_atomic(paddr, KM_USER0);
                         }
                 } else
@@ -1356,6 +1375,7 @@ void bitmap_endwrite(struct bitmap *bitmap, sector_t offset, unsigned long secto
                     bitmap->events_cleared < bitmap->mddev->events) {
                         bitmap->events_cleared = bitmap->mddev->events;
                         bitmap->need_sync = 1;
+                        sysfs_notify_dirent(bitmap->sysfs_can_clear);
                 }
 
                 if (!success && ! (*bmc & NEEDED_MASK))
@@ -1613,6 +1633,9 @@ void bitmap_destroy(mddev_t *mddev)
         if (mddev->thread)
                 mddev->thread->timeout = MAX_SCHEDULE_TIMEOUT;
 
+        if (bitmap->sysfs_can_clear)
+                sysfs_put(bitmap->sysfs_can_clear);
+
         bitmap_free(bitmap);
 }
 
@@ -1629,6 +1652,7 @@ int bitmap_create(mddev_t *mddev)
         struct file *file = mddev->bitmap_info.file;
         int err;
         sector_t start;
+        struct sysfs_dirent *bm;
 
         BUILD_BUG_ON(sizeof(bitmap_super_t) != 256);
 
@@ -1648,6 +1672,13 @@ int bitmap_create(mddev_t *mddev)
 
         bitmap->mddev = mddev;
 
+        bm = sysfs_get_dirent(mddev->kobj.sd, "bitmap");
+        if (bm) {
+                bitmap->sysfs_can_clear = sysfs_get_dirent(bm, "can_clear");
+                sysfs_put(bm);
+        } else
+                bitmap->sysfs_can_clear = NULL;
+
         bitmap->file = file;
         if (file) {
                 get_file(file);
@@ -1658,7 +1689,16 @@ int bitmap_create(mddev_t *mddev)
                 vfs_fsync(file, file->f_dentry, 1);
         }
         /* read superblock from bitmap file (this sets mddev->bitmap_info.chunksize) */
-        err = bitmap_read_sb(bitmap);
+        if (!mddev->bitmap_info.external)
+                err = bitmap_read_sb(bitmap);
+        else {
+                err = 0;
+                if (mddev->bitmap_info.chunksize == 0 ||
+                    mddev->bitmap_info.daemon_sleep == 0)
+                        /* chunksize and time_base need to be
+                         * set first. */
+                        err = -EINVAL;
+        }
         if (err)
                 goto error;
 
@@ -1777,7 +1817,8 @@ location_store(mddev_t *mddev, const char *buf, size_t len)
                                 return rv;
                         if (offset == 0)
                                 return -EINVAL;
-                        if (mddev->major_version == 0 &&
+                        if (mddev->bitmap_info.external == 0 &&
+                            mddev->major_version == 0 &&
                             offset != mddev->bitmap_info.default_offset)
                                 return -EINVAL;
                         mddev->bitmap_info.offset = offset;
@@ -1906,11 +1947,66 @@ chunksize_store(mddev_t *mddev, const char *buf, size_t len)
 static struct md_sysfs_entry bitmap_chunksize =
 __ATTR(chunksize, S_IRUGO|S_IWUSR, chunksize_show, chunksize_store);
 
+static ssize_t metadata_show(mddev_t *mddev, char *page)
+{
+        return sprintf(page, "%s\n", (mddev->bitmap_info.external
+                                      ? "external" : "internal"));
+}
+
+static ssize_t metadata_store(mddev_t *mddev, const char *buf, size_t len)
+{
+        if (mddev->bitmap ||
+            mddev->bitmap_info.file ||
+            mddev->bitmap_info.offset)
+                return -EBUSY;
+        if (strncmp(buf, "external", 8) == 0)
+                mddev->bitmap_info.external = 1;
+        else if (strncmp(buf, "internal", 8) == 0)
+                mddev->bitmap_info.external = 0;
+        else
+                return -EINVAL;
+        return len;
+}
+
+static struct md_sysfs_entry bitmap_metadata =
+__ATTR(metadata, S_IRUGO|S_IWUSR, metadata_show, metadata_store);
+
+static ssize_t can_clear_show(mddev_t *mddev, char *page)
+{
+        int len;
+        if (mddev->bitmap)
+                len = sprintf(page, "%s\n", (mddev->bitmap->need_sync ?
+                                             "false" : "true"));
+        else
+                len = sprintf(page, "\n");
+        return len;
+}
+
+static ssize_t can_clear_store(mddev_t *mddev, const char *buf, size_t len)
+{
+        if (mddev->bitmap == NULL)
+                return -ENOENT;
+        if (strncmp(buf, "false", 5) == 0)
+                mddev->bitmap->need_sync = 1;
+        else if (strncmp(buf, "true", 4) == 0) {
+                if (mddev->degraded)
+                        return -EBUSY;
+                mddev->bitmap->need_sync = 0;
+        } else
+                return -EINVAL;
+        return len;
+}
+
+static struct md_sysfs_entry bitmap_can_clear =
+__ATTR(can_clear, S_IRUGO|S_IWUSR, can_clear_show, can_clear_store);
+
 static struct attribute *md_bitmap_attrs[] = {
         &bitmap_location.attr,
         &bitmap_timeout.attr,
         &bitmap_backlog.attr,
         &bitmap_chunksize.attr,
+        &bitmap_metadata.attr,
+        &bitmap_can_clear.attr,
         NULL
 };
 struct attribute_group md_bitmap_group = {
diff --git a/drivers/md/bitmap.h b/drivers/md/bitmap.h
index 50ee4240f5db..cb821d76d1b4 100644
--- a/drivers/md/bitmap.h
+++ b/drivers/md/bitmap.h
@@ -118,16 +118,6 @@ typedef __u16 bitmap_counter_t;
                         (CHUNK_BLOCK_SHIFT(bitmap) + PAGE_COUNTER_SHIFT - 1)
 #define PAGEPTR_BLOCK_MASK(bitmap) (PAGEPTR_BLOCK_RATIO(bitmap) - 1)
 
-/*
- * on-disk bitmap:
- *
- * Use one bit per "chunk" (block set). We do the disk I/O on the bitmap
- * file a page at a time. There's a superblock at the start of the file.
- */
-
-/* map chunks (bits) to file pages - offset by the size of the superblock */
-#define CHUNK_BIT_OFFSET(chunk) ((chunk) + (sizeof(bitmap_super_t) << 3))
-
 #endif
 
 /*
@@ -250,6 +240,7 @@ struct bitmap {
         wait_queue_head_t write_wait;
         wait_queue_head_t overflow_wait;
 
+        struct sysfs_dirent *sysfs_can_clear;
 };
 
 /* the bitmap API */
diff --git a/drivers/md/md.h b/drivers/md/md.h
index fce02073f1a4..d9138885b87f 100644
--- a/drivers/md/md.h
+++ b/drivers/md/md.h
@@ -296,6 +296,7 @@ struct mddev_s
                 unsigned long           chunksize;
                 unsigned long           daemon_sleep; /* how many seconds between updates? */
                 unsigned long           max_write_behind; /* write-behind mode */
+                int                     external;
         } bitmap_info;
 
         struct list_head                all_mddevs;