dm writecache: support optional offset for start of device

Add an optional parameter "start_sector" to allow the start of the
device to be offset by the specified number of 512-byte sectors.  The
sectors below this offset are not used by the writecache device and are
left to be used for disk labels and/or userspace metadata (e.g. lvm).

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

diff --git a/Documentation/device-mapper/writecache.txt b/Documentation/device-mapper/writecache.txt
index 4424fa2..01532b3 100644 (file)
--- 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 07ea6a4..87107c9 100644 (file)
--- 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,