md/bitmap: add new 'space' attribute for bitmaps.

If we are to allow bitmaps to be resized when the array is resized,
we need to know how much space there is.

So create an attribute to store this information and set appropriate
defaults.

It can be set more precisely via sysfs, or future metadata extensions
may allow it to be recorded.

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

1 files changed, 31 insertions, 2 deletions

diff --git a/drivers/md/md.c b/drivers/md/md.c
index ac99616f48d4..9a677f2078a7 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -1197,7 +1197,10 @@ static int super_90_validate(struct mddev *mddev, struct md_rdev *rdev)
                 mddev->dev_sectors = ((sector_t)sb->size) * 2;
                 mddev->events = ev1;
                 mddev->bitmap_info.offset = 0;
+                mddev->bitmap_info.space = 0;
+                /* bitmap can use 60 K after the 4K superblocks */
                 mddev->bitmap_info.default_offset = MD_SB_BYTES >> 9;
+                mddev->bitmap_info.default_space = 64*2 - (MD_SB_BYTES >> 9);
                 mddev->reshape_backwards = 0;
 
                 if (mddev->minor_version >= 91) {
@@ -1234,9 +1237,12 @@ static int super_90_validate(struct mddev *mddev, struct md_rdev *rdev)
                 mddev->max_disks = MD_SB_DISKS;
 
                 if (sb->state & (1<<MD_SB_BITMAP_PRESENT) &&
-                    mddev->bitmap_info.file == NULL)
+                    mddev->bitmap_info.file == NULL) {
                         mddev->bitmap_info.offset =
                                 mddev->bitmap_info.default_offset;
+                        mddev->bitmap_info.space =
+                                mddev->bitmap_info.space;
+                }
 
         } else if (mddev->pers == NULL) {
                 /* Insist on good event counter while assembling, except
@@ -1677,7 +1683,12 @@ static int super_1_validate(struct mddev *mddev, struct md_rdev *rdev)
                 mddev->dev_sectors = le64_to_cpu(sb->size);
                 mddev->events = ev1;
                 mddev->bitmap_info.offset = 0;
+                mddev->bitmap_info.space = 0;
+                /* Default location for bitmap is 1K after superblock
+                 * using 3K - total of 4K
+                 */
                 mddev->bitmap_info.default_offset = 1024 >> 9;
+                mddev->bitmap_info.default_space = (4096-1024) >> 9;
                 mddev->reshape_backwards = 0;
 
                 mddev->recovery_cp = le64_to_cpu(sb->resync_offset);
@@ -1686,9 +1697,23 @@ static int super_1_validate(struct mddev *mddev, struct md_rdev *rdev)
                 mddev->max_disks =  (4096-256)/2;
 
                 if ((le32_to_cpu(sb->feature_map) & MD_FEATURE_BITMAP_OFFSET) &&
-                    mddev->bitmap_info.file == NULL )
+                    mddev->bitmap_info.file == NULL) {
                         mddev->bitmap_info.offset =
                                 (__s32)le32_to_cpu(sb->bitmap_offset);
+                        /* Metadata doesn't record how much space is available.
+                         * For 1.0, we assume we can use up to the superblock
+                         * if before, else to 4K beyond superblock.
+                         * For others, assume no change is possible.
+                         */
+                        if (mddev->minor_version > 0)
+                                mddev->bitmap_info.space = 0;
+                        else if (mddev->bitmap_info.offset > 0)
+                                mddev->bitmap_info.space =
+                                        8 - mddev->bitmap_info.offset;
+                        else
+                                mddev->bitmap_info.space =
+                                        -mddev->bitmap_info.offset;
+                }
 
                 if ((le32_to_cpu(sb->feature_map) & MD_FEATURE_RESHAPE_ACTIVE)) {
                         mddev->reshape_position = le64_to_cpu(sb->reshape_position);
@@ -5280,6 +5305,7 @@ static void md_clean(struct mddev *mddev)
         mddev->merge_check_needed = 0;
         mddev->bitmap_info.offset = 0;
         mddev->bitmap_info.default_offset = 0;
+        mddev->bitmap_info.default_space = 0;
         mddev->bitmap_info.chunksize = 0;
         mddev->bitmap_info.daemon_sleep = 0;
         mddev->bitmap_info.max_write_behind = 0;
@@ -6076,6 +6102,7 @@ static int set_array_info(struct mddev * mddev, mdu_array_info_t *info)
         set_bit(MD_CHANGE_DEVS, &mddev->flags);
 
         mddev->bitmap_info.default_offset = MD_SB_BYTES >> 9;
+        mddev->bitmap_info.default_space = 64*2 - (MD_SB_BYTES >> 9);
         mddev->bitmap_info.offset = 0;
 
         mddev->reshape_position = MaxSector;
@@ -6258,6 +6285,8 @@ static int update_array_info(struct mddev *mddev, mdu_array_info_t *info)
                                 return -EINVAL;
                         mddev->bitmap_info.offset =
                                 mddev->bitmap_info.default_offset;
+                        mddev->bitmap_info.space =
+                                mddev->bitmap_info.default_space;
                         mddev->pers->quiesce(mddev, 1);
                         rv = bitmap_create(mddev);
                         if (!rv)