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[Xen-devel] [PATCH 1 of 2 RESEND] blktap3/vhd: Import VHD support



This patch imports the VHD driver from blktap2, with all changes coming from
blktap2.5.

Signed-off-by: Thanos Makatos <thanos.makatos@xxxxxxxxxx>

diff --git a/tools/blktap3/drivers/Makefile b/tools/blktap3/drivers/Makefile
--- a/tools/blktap3/drivers/Makefile
+++ b/tools/blktap3/drivers/Makefile
@@ -95,6 +95,7 @@ LIBSRING := sring/libsring.a
 #MISC-OBJS-y := atomicio.o
 
 BLK-OBJS-y  := block-aio.o
+BLK-OBJS-y  += block-vhd.o
 # FIXME The following exist in blktap2 but not in blktap2.5.
 #BLK-OBJS-y += aes.o
 #BLK-OBJS-y += md5.o
diff --git a/tools/blktap2/drivers/block-vhd.c 
b/tools/blktap3/drivers/block-vhd.c
copy from tools/blktap2/drivers/block-vhd.c
copy to tools/blktap3/drivers/block-vhd.c
--- a/tools/blktap2/drivers/block-vhd.c
+++ b/tools/blktap3/drivers/block-vhd.c
@@ -1,5 +1,8 @@
-/* 
- * Copyright (c) 2008, XenSource Inc.
+/*
+ *
+ * Copyright (c) 2007, XenSource Inc.
+ * Copyright (c) 2010, Citrix Systems, Inc.
+ *
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -24,6 +27,10 @@
  * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
  * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
  * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+/*
+ * block-vhd.c: asynchronous vhd implementation.
  *
  * A note on write transactions:
  * Writes that require updating the BAT or bitmaps cannot be signaled
@@ -50,6 +57,8 @@
 #include <unistd.h>
 #include <sys/stat.h>
 #include <sys/ioctl.h>
+#include <uuid/uuid.h> /* For whatever reason, Linux packages this in */
+                       /* e2fsprogs-devel.                            */
 #include <string.h>    /* for memset.                                 */
 #include <libaio.h>
 #include <sys/mman.h>
@@ -59,6 +68,7 @@
 #include "tapdisk-driver.h"
 #include "tapdisk-interface.h"
 #include "tapdisk-disktype.h"
+#include "tapdisk-storage.h"
 
 unsigned int SPB;
 
@@ -72,7 +82,7 @@ unsigned int SPB;
        do {                                                            \
                DBG(TLOG_DBG, "%s: QUEUED: %" PRIu64 ", COMPLETED: %"   \
                    PRIu64", RETURNED: %" PRIu64 ", DATA_ALLOCATED: "   \
-                   "%lu, BBLK: 0x%04x\n",                              \
+                   "%u, BBLK: 0x%04x\n",                               \
                    s->vhd.file, s->queued, s->completed, s->returned,  \
                    VHD_REQS_DATA - s->vreq_free_count,                 \
                    s->bat.pbw_blk);                                    \
@@ -84,21 +94,20 @@ unsigned int SPB;
                        __FILE__, __LINE__, #_p);                       \
                DBG(TLOG_WARN, "%s:%d: FAILED ASSERTION: '%s'\n",       \
                    __FILE__, __LINE__, #_p);                           \
-               tlog_flush();                                           \
-               *(int*)0 = 0;                                           \
+               td_panic();                                             \
        }
 
 #if (DEBUGGING == 1)
   #define DBG(level, _f, _a...)      DPRINTF(_f, ##_a)
-  #define ERR(err, _f, _a...)        DPRINTF("ERROR: %d: " _f, err, ##_a)
+  #define ERR(_s, err, _f, _a...)    DPRINTF("ERROR: %d: " _f, err, ##_a)
   #define TRACE(s)                   ((void)0)
 #elif (DEBUGGING == 2)
   #define DBG(level, _f, _a...)      tlog_write(level, _f, ##_a)
-  #define ERR(err, _f, _a...)       tlog_error(err, _f, ##_a)
+  #define ERR(_s, _err, _f, _a...)   tlog_drv_error((_s)->driver, _err, _f, 
##_a)
   #define TRACE(s)                   __TRACE(s)
 #else
   #define DBG(level, _f, _a...)      ((void)0)
-  #define ERR(err, _f, _a...)        ((void)0)
+  #define ERR(_s, err, _f, _a...)    ((void)0)
   #define TRACE(s)                   ((void)0)
 #endif
 
@@ -121,6 +130,7 @@ unsigned int SPB;
 #define VHD_OP_BITMAP_READ           3
 #define VHD_OP_BITMAP_WRITE          4
 #define VHD_OP_ZERO_BM_WRITE         5
+#define VHD_OP_REDUNDANT_BM_WRITE    6
 
 #define VHD_BM_BAT_LOCKED            0
 #define VHD_BM_BAT_CLEAR             1
@@ -194,8 +204,8 @@ struct vhd_bat_state {
 };
 
 struct vhd_bitmap {
-       u32                       blk;
-       u64                       seqno;       /* lru sequence number */
+       uint32_t                  blk;
+       uint64_t                  seqno;       /* lru sequence number */
        vhd_flag_t                status;
 
        char                     *map;         /* map should only be modified
@@ -220,15 +230,16 @@ struct vhd_state {
 
         /* VHD stuff */
        vhd_context_t             vhd;
-       u32                       spp;         /* sectors per page */
-        u32                       spb;         /* sectors per block */
-        u64                       next_db;     /* pointer to the next 
+       uint32_t                  spp;         /* sectors per page */
+       uint32_t                  spb;         /* sectors per block */
+       uint64_t                  first_db;    /* pointer to datablock 0 */
+       uint64_t                  next_db;     /* pointer to the next 
                                                * (unallocated) datablock */
 
        struct vhd_bat_state      bat;
 
-       u64                       bm_lru;      /* lru sequence number */
-       u32                       bm_secs;     /* size of bitmap, in sectors */
+       uint64_t                  bm_lru;      /* lru sequence number */
+       uint32_t                  bm_secs;     /* size of bitmap, in sectors */
        struct vhd_bitmap        *bitmap[VHD_CACHE_SIZE];
 
        int                       bm_free_count;
@@ -239,6 +250,12 @@ struct vhd_state {
        struct vhd_request       *vreq_free[VHD_REQS_DATA];
        struct vhd_request        vreq_list[VHD_REQS_DATA];
 
+       /* for redundant bitmap writes */
+       int                       padbm_size;
+       char                     *padbm_buf;
+       long int                  debug_skipped_redundant_writes;
+       long int                  debug_done_redundant_writes;
+
        td_driver_t              *driver;
 
        uint64_t                  queued;
@@ -274,7 +291,7 @@ vhd_initialize(struct vhd_state *s)
                _vhd_zsize += VHD_BLOCK_SIZE;
 
        _vhd_zeros = mmap(0, _vhd_zsize, PROT_READ,
-                         MAP_SHARED | MAP_ANON, -1, 0);
+                         MAP_SHARED | MAP_ANONYMOUS, -1, 0);
        if (_vhd_zeros == MAP_FAILED) {
                EPRINTF("vhd_initialize failed: %d\n", -errno);
                _vhd_zeros = NULL;
@@ -292,6 +309,7 @@ vhd_free(struct vhd_state *s)
        if (_vhd_master != s || !_vhd_zeros)
                return;
 
+       free(s->padbm_buf);
        munmap(_vhd_zeros, _vhd_zsize);
        _vhd_zsize  = 0;
        _vhd_zeros  = NULL;
@@ -333,23 +351,23 @@ static int
 vhd_kill_footer(struct vhd_state *s)
 {
        int err;
-       off_t end;
-       char *zeros;
+       off64_t end;
+       void *zeros;
 
        if (s->vhd.footer.type == HD_TYPE_FIXED)
                return 0;
 
-       err = posix_memalign((void **)&zeros, 512, 512);
+       err = posix_memalign(&zeros, 512, 512);
        if (err)
                return -err;
 
        err = 1;
        memset(zeros, 0xc7c7c7c7, 512);
 
-       if ((end = lseek(s->vhd.fd, 0, SEEK_END)) == -1)
+       if ((end = lseek64(s->vhd.fd, 0, SEEK_END)) == -1)
                goto fail;
 
-       if (lseek(s->vhd.fd, (end - 512), SEEK_SET) == -1)
+       if (lseek64(s->vhd.fd, (end - 512), SEEK_SET) == -1)
                goto fail;
 
        if (write(s->vhd.fd, zeros, 512) != 512)
@@ -368,7 +386,7 @@ static inline int
 find_next_free_block(struct vhd_state *s)
 {
        int err;
-       off_t eom;
+       off64_t eom;
        uint32_t i, entry;
 
        err = vhd_end_of_headers(&s->vhd, &eom);
@@ -376,6 +394,9 @@ find_next_free_block(struct vhd_state *s
                return err;
 
        s->next_db = secs_round_up(eom);
+       s->first_db = s->next_db;
+       if ((s->first_db + s->bm_secs) % s->spp)
+               s->first_db += (s->spp - ((s->first_db + s->bm_secs) % s->spp));
 
        for (i = 0; i < s->bat.bat.entries; i++) {
                entry = bat_entry(s, i);
@@ -398,12 +419,11 @@ vhd_free_bat(struct vhd_state *s)
 static int
 vhd_initialize_bat(struct vhd_state *s)
 {
-       int err, psize, batmap_required, i;
+       int err, batmap_required, i;
+       void *buf;
 
        memset(&s->bat, 0, sizeof(struct vhd_bat));
 
-       psize = getpagesize();
-
        err = vhd_read_bat(&s->vhd, &s->bat.bat);
        if (err) {
                EPRINTF("%s: reading bat: %d\n", s->vhd.file, err);
@@ -436,12 +456,11 @@ vhd_initialize_bat(struct vhd_state *s)
                                        s->vhd.file);
        }
 
-       err = posix_memalign((void **)&s->bat.bat_buf,
-                            VHD_SECTOR_SIZE, VHD_SECTOR_SIZE);
-       if (err) {
-               s->bat.bat_buf = NULL;
+       err = posix_memalign(&buf, VHD_SECTOR_SIZE, VHD_SECTOR_SIZE);
+       if (err)
                goto fail;
-       }
+
+       s->bat.bat_buf = buf;
 
        return 0;
 
@@ -471,6 +490,7 @@ vhd_initialize_bitmap_cache(struct vhd_s
 {
        int i, err, map_size;
        struct vhd_bitmap *bm;
+       void *map, *shadow;
 
        memset(s->bitmap_list, 0, sizeof(struct vhd_bitmap) * VHD_CACHE_SIZE);
 
@@ -481,17 +501,17 @@ vhd_initialize_bitmap_cache(struct vhd_s
        for (i = 0; i < VHD_CACHE_SIZE; i++) {
                bm = s->bitmap_list + i;
 
-               err = posix_memalign((void **)&bm->map, 512, map_size);
-               if (err) {
-                       bm->map = NULL;
+               err = posix_memalign(&map, 512, map_size);
+               if (err)
                        goto fail;
-               }
-
-               err = posix_memalign((void **)&bm->shadow, 512, map_size);
-               if (err) {
-                       bm->shadow = NULL;
+
+               bm->map = map;
+
+               err = posix_memalign(&shadow, 512, map_size);
+               if (err)
                        goto fail;
-               }
+
+               bm->shadow = shadow;
 
                memset(bm->map, 0, map_size);
                memset(bm->shadow, 0, map_size);
@@ -508,6 +528,8 @@ fail:
 static int
 vhd_initialize_dynamic_disk(struct vhd_state *s)
 {
+       uint32_t bm_size;
+       void *buf;
        int err;
 
        err = vhd_get_header(&s->vhd);
@@ -527,6 +549,21 @@ vhd_initialize_dynamic_disk(struct vhd_s
        s->spb     = s->vhd.header.block_size >> VHD_SECTOR_SHIFT;
        s->bm_secs = secs_round_up_no_zero(s->spb >> 3);
 
+       s->padbm_size = (s->bm_secs / getpagesize()) * getpagesize();
+       if (s->bm_secs % getpagesize())
+               s->padbm_size += getpagesize();
+
+       err = posix_memalign(&buf, 512, s->padbm_size);
+       if (err)
+               return -err;
+
+       s->padbm_buf = buf;
+       bm_size = s->bm_secs << VHD_SECTOR_SHIFT;
+       memset(s->padbm_buf, 0, s->padbm_size - bm_size);
+       memset(s->padbm_buf + (s->padbm_size - bm_size), ~0, bm_size);
+       s->debug_skipped_redundant_writes = 0;
+       s->debug_done_redundant_writes = 0;
+
        if (test_vhd_flag(s->flags, VHD_FLAG_OPEN_NO_CACHE))
                return 0;
 
@@ -616,6 +653,9 @@ static int
        o_flags = ((test_vhd_flag(flags, VHD_FLAG_OPEN_RDONLY)) ? 
                   VHD_OPEN_RDONLY : VHD_OPEN_RDWR);
 
+       if (test_vhd_flag(flags, VHD_FLAG_OPEN_STRICT))
+               set_vhd_flag(o_flags, VHD_OPEN_STRICT);
+
        err = vhd_open(&s->vhd, name, o_flags);
        if (err) {
                libvhd_set_log_level(1);
@@ -650,8 +690,7 @@ static int
        driver->info.sector_size = VHD_SECTOR_SIZE;
        driver->info.info        = 0;
 
-        DBG(TLOG_INFO, "vhd_open: done (sz:%"PRIu64", sct:%"PRIu64
-            ", inf:%u)\n",
+        DBG(TLOG_INFO, "vhd_open: done (sz:%"PRIu64", sct:%lu, inf:%u)\n",
            driver->info.size, driver->info.sector_size, driver->info.info);
 
        if (test_vhd_flag(flags, VHD_FLAG_OPEN_STRICT) && 
@@ -692,6 +731,8 @@ static int
                              VHD_FLAG_OPEN_NO_CACHE);
 
        /* pre-allocate for all but NFS and LVM storage */
+       driver->storage = tapdisk_storage_type(name);
+
        if (driver->storage != TAPDISK_STORAGE_TYPE_NFS &&
            driver->storage != TAPDISK_STORAGE_TYPE_LVM)
                vhd_flags |= VHD_FLAG_OPEN_PREALLOCATE;
@@ -726,11 +767,14 @@ static int
 {
        int err;
        struct vhd_state *s;
-       struct vhd_bitmap *bm;
        
        DBG(TLOG_WARN, "vhd_close\n");
        s = (struct vhd_state *)driver->data;
 
+       DPRINTF("gaps written/skipped: %ld/%ld\n", 
+                       s->debug_done_redundant_writes,
+                       s->debug_skipped_redundant_writes);
+
        /* don't write footer if tapdisk is read-only */
        if (test_vhd_flag(s->flags, VHD_FLAG_OPEN_RDONLY))
                goto free;
@@ -770,10 +814,9 @@ static int
 
 int
 vhd_validate_parent(td_driver_t *child_driver,
-                   td_driver_t *parent_driver, td_flag_t flags)
+                   td_driver_t *parent_driver,
+            __attribute__((unused)) td_flag_t flags)
 {
-       uint32_t status;
-       struct stat stats;
        struct vhd_state *child  = (struct vhd_state *)child_driver->data;
        struct vhd_state *parent;
 
@@ -807,7 +850,7 @@ vhd_validate_parent(td_driver_t *child_d
        }
        */
 
-       if (vhd_uuid_compare(&child->vhd.header.prt_uuid, 
&parent->vhd.footer.uuid)) {
+       if (uuid_compare(child->vhd.header.prt_uuid, parent->vhd.footer.uuid)) {
                DPRINTF("ERROR: %s: %s, %s: parent uuid has changed since "
                        "snapshot.  Child image no longer valid.\n",
                        __func__, child->vhd.file, parent->vhd.file);
@@ -838,12 +881,10 @@ vhd_get_parent_id(td_driver_t *driver, t
        if (err)
                return err;
 
-       id->name       = parent;
-       id->drivertype = DISK_TYPE_VHD;
-       if (vhd_parent_raw(&s->vhd)) {
-               DPRINTF("VHD: parent is raw\n");
-               id->drivertype = DISK_TYPE_AIO;
-       }
+       id->name   = parent;
+       id->type   = vhd_parent_raw(&s->vhd) ? DISK_TYPE_AIO : DISK_TYPE_VHD;
+       id->flags |= TD_OPEN_SHAREABLE|TD_OPEN_RDONLY;
+
        return 0;
 }
 
@@ -1034,7 +1075,7 @@ static struct vhd_bitmap *
 remove_lru_bitmap(struct vhd_state *s)
 {
        int i, idx = 0;
-       u64 seq = s->bm_lru;
+       uint64_t seq = s->bm_lru;
        struct vhd_bitmap *bm, *lru = NULL;
 
        for (i = 0; i < VHD_CACHE_SIZE; i++) {
@@ -1138,7 +1179,7 @@ free_vhd_bitmap(struct vhd_state *s, str
 static int
 read_bitmap_cache(struct vhd_state *s, uint64_t sector, uint8_t op)
 {
-       u32 blk, sec;
+       uint32_t blk, sec;
        struct vhd_bitmap *bm;
 
        /* in fixed disks, every block is present */
@@ -1186,7 +1227,7 @@ read_bitmap_cache_span(struct vhd_state 
                       uint64_t sector, int nr_secs, int value)
 {
        int ret;
-       u32 blk, sec;
+       uint32_t blk, sec;
        struct vhd_bitmap *bm;
 
        /* in fixed disks, every block is present */
@@ -1285,9 +1326,9 @@ static int
 schedule_bat_write(struct vhd_state *s)
 {
        int i;
-       u32 blk;
+       uint32_t blk;
        char *buf;
-       u64 offset;
+       uint64_t offset;
        struct vhd_request *req;
 
        ASSERT(bat_locked(s));
@@ -1299,10 +1340,10 @@ schedule_bat_write(struct vhd_state *s)
        init_vhd_request(s, req);
        memcpy(buf, &bat_entry(s, blk - (blk % 128)), 512);
 
-       ((u32 *)buf)[blk % 128] = s->bat.pbw_offset;
+       ((uint32_t *)buf)[blk % 128] = s->bat.pbw_offset;
 
        for (i = 0; i < 128; i++)
-               BE32_OUT(&((u32 *)buf)[i]);
+               BE32_OUT(&((uint32_t *)buf)[i]);
 
        offset         = s->vhd.header.table_offset + (blk - (blk % 128)) * 4;
        req->treq.secs = 1;
@@ -1343,6 +1384,55 @@ schedule_zero_bm_write(struct vhd_state 
        aio_write(s, req, offset);
 }
 
+/* This is a performance optimization. When writing sequentially into full 
+ * blocks, skipping (up-to-date) bitmaps causes an approx. 25% reduction in 
+ * throughput. To prevent skipping, we issue redundant writes into the 
(padded) 
+ * bitmap area just to make all writes sequential. This will help VHDs on raw 
+ * block devices, while the FS-based VHDs shouldn't suffer much.
+ *
+ * Note that it only makes sense to perform this reduntant bitmap write if the 
+ * block is completely full (i.e. the batmap entry is set). If the block is 
not 
+ * completely full then one of the following two things will be true:
+ *  1. we'll either be allocating new sectors in this block and writing its
+ *     bitmap transactionally, which will be slow anyways; or
+ *  2. the IO will be skipping over the unallocated sectors again, so the
+ *     pattern will not be sequential anyways
+ * In either case a redundant bitmap write becomes pointless. This fact 
+ * simplifies the implementation of redundant writes: since we know the bitmap 
+ * cannot be updated by anyone else, we don't have to worry about transactions 
+ * or potential write conflicts.
+ * */
+static void
+schedule_redundant_bm_write(struct vhd_state *s, uint32_t blk)
+{
+       uint64_t offset;
+       struct vhd_request *req;
+
+       ASSERT(s->vhd.footer.type != HD_TYPE_FIXED);
+       ASSERT(test_batmap(s, blk));
+
+       req = alloc_vhd_request(s);
+       if (!req) 
+               return;
+
+       req->treq.buf = s->padbm_buf;
+
+       offset = bat_entry(s, blk);
+       ASSERT(offset != DD_BLK_UNUSED);
+       offset <<= VHD_SECTOR_SHIFT;
+       offset -= s->padbm_size - (s->bm_secs << VHD_SECTOR_SHIFT);
+
+       req->op        = VHD_OP_REDUNDANT_BM_WRITE;
+       req->treq.sec  = blk * s->spb;
+       req->treq.secs = s->padbm_size >> VHD_SECTOR_SHIFT;
+       req->next      = NULL;
+
+       DBG(TLOG_DBG, "blk: %u, writing redundant bitmap at %" PRIu64 "\n",
+           blk, offset);
+
+       aio_write(s, req, offset);
+}
+
 static int
 update_bat(struct vhd_state *s, uint32_t blk)
 {
@@ -1380,10 +1470,10 @@ update_bat(struct vhd_state *s, uint32_t
 static int
 allocate_block(struct vhd_state *s, uint32_t blk)
 {
-       char *zeros;
        int err, gap;
        uint64_t offset, size;
        struct vhd_bitmap *bm;
+       ssize_t count;
 
        ASSERT(bat_entry(s, blk) == DD_BLK_UNUSED);
 
@@ -1410,15 +1500,16 @@ allocate_block(struct vhd_state *s, uint
            blk, s->bat.pbw_offset);
 
        if (lseek(s->vhd.fd, offset, SEEK_SET) == (off_t)-1) {
-               ERR(errno, "lseek failed\n");
+               ERR(s, -errno, "lseek failed\n");
                return -errno;
        }
 
-       size = vhd_sectors_to_bytes(s->spb + s->bm_secs + gap);
-       err  = write(s->vhd.fd, vhd_zeros(size), size);
-       if (err != size) {
-               err = (err == -1 ? -errno : -EIO);
-               ERR(err, "write failed");
+       size  = vhd_sectors_to_bytes(s->spb + s->bm_secs + gap);
+       count = write(s->vhd.fd, vhd_zeros(size), size);
+       if (count != size) {
+               err = count < 0 ? -errno : -ENOSPC;
+               ERR(s, -errno,
+                   "write failed (%zd, offset %"PRIu64")\n", count, offset);
                return err;
        }
 
@@ -1445,8 +1536,8 @@ allocate_block(struct vhd_state *s, uint
 static int 
 schedule_data_read(struct vhd_state *s, td_request_t treq, vhd_flag_t flags)
 {
-       u64 offset;
-       u32 blk = 0, sec = 0;
+       uint64_t offset;
+       uint32_t blk = 0, sec = 0;
        struct vhd_bitmap  *bm;
        struct vhd_request *req;
 
@@ -1490,8 +1581,8 @@ static int
 schedule_data_write(struct vhd_state *s, td_request_t treq, vhd_flag_t flags)
 {
        int err;
-       u64 offset;
-       u32 blk = 0, sec = 0;
+       uint64_t offset;
+       uint32_t blk = 0, sec = 0;
        struct vhd_bitmap  *bm = NULL;
        struct vhd_request *req;
 
@@ -1539,7 +1630,11 @@ schedule_data_write(struct vhd_state *s,
                        set_vhd_flag(req->flags, VHD_FLAG_REQ_QUEUED);
                } else
                        add_to_transaction(&bm->tx, req);
-       }
+       } else if (sec == 0 &&  /* first sector inside data block */
+                  s->vhd.footer.type != HD_TYPE_FIXED && 
+                  bat_entry(s, blk) != s->first_db &&
+                  test_batmap(s, blk))
+               schedule_redundant_bm_write(s, blk);
 
        aio_write(s, req, offset);
 
@@ -1554,7 +1649,7 @@ static int
 schedule_bitmap_read(struct vhd_state *s, uint32_t blk)
 {
        int err;
-       u64 offset;
+       uint64_t offset;
        struct vhd_bitmap  *bm;
        struct vhd_request *req = NULL;
 
@@ -1596,7 +1691,7 @@ schedule_bitmap_read(struct vhd_state *s
 static void
 schedule_bitmap_write(struct vhd_state *s, uint32_t blk)
 {
-       u64 offset;
+       uint64_t offset;
        struct vhd_bitmap  *bm;
        struct vhd_request *req;
 
@@ -1641,7 +1736,7 @@ schedule_bitmap_write(struct vhd_state *
 static int
 __vhd_queue_request(struct vhd_state *s, uint8_t op, td_request_t treq)
 {
-       u32 blk;
+       uint32_t blk;
        struct vhd_bitmap  *bm;
        struct vhd_request *req;
 
@@ -1767,7 +1862,6 @@ vhd_queue_write(td_driver_t *driver, td_
 
                case VHD_BM_BAT_LOCKED:
                        err = -EBUSY;
-                       clone.blocked = 1;
                        goto fail;
 
                case VHD_BM_BAT_CLEAR:
@@ -1860,9 +1954,9 @@ signal_completion(struct vhd_request *li
 static void
 start_new_bitmap_transaction(struct vhd_state *s, struct vhd_bitmap *bm)
 {
-       int i, error = 0;
        struct vhd_transaction *tx;
        struct vhd_request *r, *next;
+       int i;
 
        if (!bm->queue.head)
                return;
@@ -1885,7 +1979,7 @@ start_new_bitmap_transaction(struct vhd_
                if (test_vhd_flag(r->flags, VHD_FLAG_REQ_FINISHED)) {
                        tx->finished++;
                        if (!r->error) {
-                               u32 sec = r->treq.sec % s->spb;
+                               uint32_t sec = r->treq.sec % s->spb;
                                for (i = 0; i < r->treq.secs; i++)
                                        vhd_bitmap_set(&s->vhd,
                                                       bm->shadow, sec + i);
@@ -2027,7 +2121,7 @@ finish_bat_write(struct vhd_request *req
 static void
 finish_zero_bm_write(struct vhd_request *req)
 {
-       u32 blk;
+       uint32_t blk;
        struct vhd_bitmap *bm;
        struct vhd_transaction *tx = req->tx;
        struct vhd_state *s = req->state;
@@ -2058,10 +2152,30 @@ finish_zero_bm_write(struct vhd_request 
                finish_data_transaction(s, bm);
 }
 
+static int
+finish_redundant_bm_write(struct vhd_request *req)
+{
+       /* uint32_t blk; */
+       struct vhd_state *s = (struct vhd_state *) req->state;
+
+       s->returned++;
+       TRACE(s);       
+       /* blk = req->treq.sec / s->spb;
+          DBG(TLOG_DBG, "blk: %u\n", blk); */
+
+       if (req->error) {
+               ERR(s, req->error, "lsec: 0x%08"PRIx64, req->treq.sec);
+       }
+       free_vhd_request(s, req);
+       s->debug_done_redundant_writes++;
+       return 0;
+}
+
+
 static void
 finish_bitmap_read(struct vhd_request *req)
 {
-       u32 blk;
+       uint32_t blk;
        struct vhd_bitmap  *bm;
        struct vhd_request *r, *next;
        struct vhd_state   *s = req->state;
@@ -2113,7 +2227,7 @@ finish_bitmap_read(struct vhd_request *r
 static void
 finish_bitmap_write(struct vhd_request *req)
 {
-       u32 blk;
+       uint32_t blk;
        struct vhd_bitmap  *bm;
        struct vhd_transaction *tx;
        struct vhd_state *s = req->state;
@@ -2156,7 +2270,7 @@ finish_data_write(struct vhd_request *re
        set_vhd_flag(req->flags, VHD_FLAG_REQ_FINISHED);
 
        if (tx) {
-               u32 blk, sec;
+               uint32_t blk, sec;
                struct vhd_bitmap *bm;
 
                blk = req->treq.sec / s->spb;
@@ -2199,7 +2313,7 @@ vhd_complete(void *arg, struct tiocb *ti
        req->error = err;
 
        if (req->error)
-               ERR(req->error, "%s: op: %u, lsec: %"PRIu64", secs: %u, "
+               ERR(s, req->error, "%s: op: %u, lsec: %"PRIu64", secs: %u, "
                    "nbytes: %lu, blk: %"PRIu64", blk_offset: %u",
                    s->vhd.file, req->op, req->treq.sec, req->treq.secs,
                    io->u.c.nbytes, req->treq.sec / s->spb,
@@ -2226,6 +2340,10 @@ vhd_complete(void *arg, struct tiocb *ti
                finish_zero_bm_write(req);
                break;
 
+       case VHD_OP_REDUNDANT_BM_WRITE:
+               finish_redundant_bm_write(req);
+               break;
+
        case VHD_OP_BAT_WRITE:
                finish_bat_write(req);
                break;
@@ -2250,14 +2368,15 @@ vhd_debug(td_driver_t *driver)
        DBG(TLOG_WARN, "READS: 0x%08"PRIx64", AVG_READ_SIZE: %f\n",
            s->reads, (s->reads ? ((float)s->read_size / s->reads) : 0.0));
 
-       DBG(TLOG_WARN, "ALLOCATED REQUESTS: (%lu total)\n", VHD_REQS_DATA);
+       DBG(TLOG_WARN, "ALLOCATED REQUESTS: (%u total)\n", VHD_REQS_DATA);
        for (i = 0; i < VHD_REQS_DATA; i++) {
                struct vhd_request *r = &s->vreq_list[i];
                td_request_t *t       = &r->treq;
+               const char *vname     = t->vreq ? t->vreq->name: NULL;
                if (t->secs)
-                       DBG(TLOG_WARN, "%d: id: 0x%04"PRIx64", err: %d, op: %d,"
+                       DBG(TLOG_WARN, "%d: vreq: %s.%d, err: %d, op: %d,"
                            " lsec: 0x%08"PRIx64", flags: %d, this: %p, "
-                           "next: %p, tx: %p\n", i, t->id, r->error, r->op,
+                           "next: %p, tx: %p\n", i, vname, t->sidx, r->error, 
r->op,
                            t->sec, r->flags, r, r->next, r->tx);
        }
 

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