Merge tag 'for-4.18/dm-fixes-2' of git://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm

Pull device mapper fix from Mike Snitzer:
 "Fix DM writecache target to allow an optional offset to the start of
  the data and metadata area.

  This allows userspace tools (e.g. LVM2) to place a header and metadata
  at the front of the writecache device for its use"

* tag 'for-4.18/dm-fixes-2' of git://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm:
  dm writecache: support optional offset for start of device

2 files changed, 31 insertions, 14 deletions

diff --git a/Documentation/device-mapper/writecache.txt b/Documentation/device-mapper/writecache.txt
index 4424fa2c67d7..01532b3008ae 100644
--- a/Documentation/device-mapper/writecache.txt
+++ b/Documentation/device-mapper/writecache.txt
@@ -15,6 +15,8 @@ Constructor parameters:
    size)
 5. the number of optional parameters (the parameters with an argument
    count as two)
+        start_sector n          (default: 0)
+                offset from the start of cache device in 512-byte sectors
         high_watermark n        (default: 50)
                 start writeback when the number of used blocks reach this
                 watermark
diff --git a/drivers/md/dm-writecache.c b/drivers/md/dm-writecache.c
index 07ea6a48aac6..87107c995cb5 100644
--- a/drivers/md/dm-writecache.c
+++ b/drivers/md/dm-writecache.c
@@ -136,6 +136,7 @@ struct dm_writecache {
         struct dm_target *ti;
         struct dm_dev *dev;
         struct dm_dev *ssd_dev;
+        sector_t start_sector;
         void *memory_map;
         uint64_t memory_map_size;
         size_t metadata_sectors;
@@ -293,6 +294,10 @@ static int persistent_memory_claim(struct dm_writecache *wc)
         }
 
         dax_read_unlock(id);
+
+        wc->memory_map += (size_t)wc->start_sector << SECTOR_SHIFT;
+        wc->memory_map_size -= (size_t)wc->start_sector << SECTOR_SHIFT;
+
         return 0;
 err3:
         kvfree(pages);
@@ -311,7 +316,7 @@ static int persistent_memory_claim(struct dm_writecache *wc)
 static void persistent_memory_release(struct dm_writecache *wc)
 {
         if (wc->memory_vmapped)
-                vunmap(wc->memory_map);
+                vunmap(wc->memory_map - ((size_t)wc->start_sector << SECTOR_SHIFT));
 }
 
 static struct page *persistent_memory_page(void *addr)
@@ -359,7 +364,7 @@ static void *memory_data(struct dm_writecache *wc, struct wc_entry *e)
 
 static sector_t cache_sector(struct dm_writecache *wc, struct wc_entry *e)
 {
-        return wc->metadata_sectors +
+        return wc->start_sector + wc->metadata_sectors +
                 ((sector_t)e->index << (wc->block_size_bits - SECTOR_SHIFT));
 }
 
@@ -471,6 +476,7 @@ static void ssd_commit_flushed(struct dm_writecache *wc)
                 if (unlikely(region.sector + region.count > wc->metadata_sectors))
                         region.count = wc->metadata_sectors - region.sector;
 
+                region.sector += wc->start_sector;
                 atomic_inc(&endio.count);
                 req.bi_op = REQ_OP_WRITE;
                 req.bi_op_flags = REQ_SYNC;
@@ -1946,14 +1952,6 @@ static int writecache_ctr(struct dm_target *ti, unsigned argc, char **argv)
         }
         wc->memory_map_size = i_size_read(wc->ssd_dev->bdev->bd_inode);
 
-        if (WC_MODE_PMEM(wc)) {
-                r = persistent_memory_claim(wc);
-                if (r) {
-                        ti->error = "Unable to map persistent memory for cache";
-                        goto bad;
-                }
-        }
-
         /*
          * Parse the cache block size
          */
@@ -1982,7 +1980,16 @@ static int writecache_ctr(struct dm_target *ti, unsigned argc, char **argv)
 
         while (opt_params) {
                 string = dm_shift_arg(&as), opt_params--;
-                if (!strcasecmp(string, "high_watermark") && opt_params >= 1) {
+                if (!strcasecmp(string, "start_sector") && opt_params >= 1) {
+                        unsigned long long start_sector;
+                        string = dm_shift_arg(&as), opt_params--;
+                        if (sscanf(string, "%llu%c", &start_sector, &dummy) != 1)
+                                goto invalid_optional;
+                        wc->start_sector = start_sector;
+                        if (wc->start_sector != start_sector ||
+                            wc->start_sector >= wc->memory_map_size >> SECTOR_SHIFT)
+                                goto invalid_optional;
+                } else if (!strcasecmp(string, "high_watermark") && opt_params >= 1) {
                         string = dm_shift_arg(&as), opt_params--;
                         if (sscanf(string, "%d%c", &high_wm_percent, &dummy) != 1)
                                 goto invalid_optional;
@@ -2039,12 +2046,20 @@ invalid_optional:
                 goto bad;
         }
 
-        if (!WC_MODE_PMEM(wc)) {
+        if (WC_MODE_PMEM(wc)) {
+                r = persistent_memory_claim(wc);
+                if (r) {
+                        ti->error = "Unable to map persistent memory for cache";
+                        goto bad;
+                }
+        } else {
                 struct dm_io_region region;
                 struct dm_io_request req;
                 size_t n_blocks, n_metadata_blocks;
                 uint64_t n_bitmap_bits;
 
+                wc->memory_map_size -= (uint64_t)wc->start_sector << SECTOR_SHIFT;
+
                 bio_list_init(&wc->flush_list);
                 wc->flush_thread = kthread_create(writecache_flush_thread, wc, "dm_writecache_flush");
                 if (IS_ERR(wc->flush_thread)) {
@@ -2097,7 +2112,7 @@ invalid_optional:
                 }
 
                 region.bdev = wc->ssd_dev->bdev;
-                region.sector = 0;
+                region.sector = wc->start_sector;
                 region.count = wc->metadata_sectors;
                 req.bi_op = REQ_OP_READ;
                 req.bi_op_flags = REQ_SYNC;
@@ -2265,7 +2280,7 @@ static void writecache_status(struct dm_target *ti, status_type_t type,
 
 static struct target_type writecache_target = {
         .name                   = "writecache",
-        .version                = {1, 0, 0},
+        .version                = {1, 1, 0},
         .module                 = THIS_MODULE,
         .ctr                    = writecache_ctr,
         .dtr                    = writecache_dtr,