[Qemu-devel] [PATCH V4] block/iscsi: allow caching of the allocation map

[Qemu-devel] [PATCH V4] block/iscsi: allow caching of the allocation map

[Peter Lieven]

until now the allocation map was used only as a hint if a cluster
is allocated or not. If a block was not allocated (or Qemu had
no info about the allocation status) a get_block_status call was
issued to check the allocation status and possibly avoid
a subsequent read of unallocated sectors. If a block known to be
allocated the get_block_status call was omitted. In the other case
a get_block_status call was issued before every read to avoid
the necessity for a consistent allocation map. To avoid the
potential overhead of calling get_block_status for each and
every read request this took only place for the bigger requests.

This patch enhances this mechanism to cache the allocation
status and avoid calling get_block_status for blocks where
the allocation status has been queried before. This allows
for bypassing the read request even for smaller requests and
additionally omits calling get_block_status for known to be
unallocated blocks.

Signed-off-by: Peter Lieven <pl@kamp.de>
---
v3->v4: - added comment to iscsi_allocmap_set_unallocated [Paolo]
        - rebased to current master
v2->v3: - fix wording errors [Fam]
        - reinit allocmap only if allocmap is present in
          bdrv_reopen_commit
v1->v2: - add more comments [Fam]
        - free allocmap if allocation of allocmap_valid fails [Fam]
        - fix indent and whitespace errors [Fam]
        - account for cache mode changes on reopen

 block/iscsi.c | 240 +++++++++++++++++++++++++++++++++++++++++++++-------------
 1 file changed, 188 insertions(+), 52 deletions(-)

diff --git a/block/iscsi.c b/block/iscsi.c
index 9bb5ff6..0cdcedb 100644
--- a/block/iscsi.c
+++ b/block/iscsi.c
@@ -2,7 +2,7 @@
  * QEMU Block driver for iSCSI images
  *
  * Copyright (c) 2010-2011 Ronnie Sahlberg <ronniesahlberg@gmail.com>
- * Copyright (c) 2012-2015 Peter Lieven <pl@kamp.de>
+ * Copyright (c) 2012-2016 Peter Lieven <pl@kamp.de>
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -62,7 +62,23 @@ typedef struct IscsiLun {
     struct scsi_inquiry_logical_block_provisioning lbp;
     struct scsi_inquiry_block_limits bl;
     unsigned char *zeroblock;
-    unsigned long *allocationmap;
+    /* The allocmap tracks which clusters (pages) on the iSCSI target are
+     * allocated and which are not. In case a target returns zeros for
+     * unallocated pages (iscsilun->lprz) we can directly return zeros instead
+     * of reading zeros over the wire if a read request falls within an
+     * unallocated block. As there are 3 possible states we need 2 bitmaps to
+     * track. allocmap_valid keeps track if QEMU's information about a page is
+     * valid. allocmap tracks if a page is allocated or not. In case QEMU has no
+     * valid information about a page the corresponding allocmap entry should be
+     * switched to unallocated as well to force a new lookup of the allocation
+     * status as lookups are generally skipped if a page is suspect to be
+     * allocated. If a iSCSI target is opened with cache.direct = on the
+     * allocmap_valid does not exist turning all cached information invalid so
+     * that a fresh lookup is made for any page even if allocmap entry returns
+     * it's unallocated. */
+    unsigned long *allocmap;
+    unsigned long *allocmap_valid;
+    long allocmap_size;
     int cluster_sectors;
     bool use_16_for_rw;
     bool write_protected;
@@ -423,37 +439,135 @@ static bool is_sector_request_lun_aligned(int64_t sector_num, int nb_sectors,
                                        iscsilun);
 }
 
-static unsigned long *iscsi_allocationmap_init(IscsiLun *iscsilun)
+static void iscsi_allocmap_free(IscsiLun *iscsilun)
 {
-    return bitmap_try_new(DIV_ROUND_UP(sector_lun2qemu(iscsilun->num_blocks,
-                                                       iscsilun),
-                                       iscsilun->cluster_sectors));
+    g_free(iscsilun->allocmap);
+    g_free(iscsilun->allocmap_valid);
+    iscsilun->allocmap = NULL;
+    iscsilun->allocmap_valid = NULL;
 }
 
-static void iscsi_allocationmap_set(IscsiLun *iscsilun, int64_t sector_num,
-                                    int nb_sectors)
+
+static int iscsi_allocmap_init(IscsiLun *iscsilun, int open_flags)
 {
-    if (iscsilun->allocationmap == NULL) {
-        return;
+    iscsi_allocmap_free(iscsilun);
+
+    iscsilun->allocmap_size =
+        DIV_ROUND_UP(sector_lun2qemu(iscsilun->num_blocks, iscsilun),
+                     iscsilun->cluster_sectors);
+
+    iscsilun->allocmap = bitmap_try_new(iscsilun->allocmap_size);
+    if (!iscsilun->allocmap) {
+        return -ENOMEM;
     }
-    bitmap_set(iscsilun->allocationmap,
-               sector_num / iscsilun->cluster_sectors,
-               DIV_ROUND_UP(nb_sectors, iscsilun->cluster_sectors));
+
+    if (open_flags & BDRV_O_NOCACHE) {
+        /* in case that cache.direct = on all allocmap entries are
+         * treated as invalid to force a relookup of the block
+         * status on every read request */
+        return 0;
+    }
+
+    iscsilun->allocmap_valid = bitmap_try_new(iscsilun->allocmap_size);
+    if (!iscsilun->allocmap_valid) {
+        /* if we are under memory pressure free the allocmap as well */
+        iscsi_allocmap_free(iscsilun);
+        return -ENOMEM;
+    }
+
+    return 0;
 }
 
-static void iscsi_allocationmap_clear(IscsiLun *iscsilun, int64_t sector_num,
-                                      int nb_sectors)
+static void
+iscsi_allocmap_update(IscsiLun *iscsilun, int64_t sector_num,
+                      int nb_sectors, bool allocated, bool valid)
 {
     int64_t cluster_num, nb_clusters;
-    if (iscsilun->allocationmap == NULL) {
+
+    if (iscsilun->allocmap == NULL) {
         return;
     }
     cluster_num = DIV_ROUND_UP(sector_num, iscsilun->cluster_sectors);
     nb_clusters = (sector_num + nb_sectors) / iscsilun->cluster_sectors
                   - cluster_num;
-    if (nb_clusters > 0) {
-        bitmap_clear(iscsilun->allocationmap, cluster_num, nb_clusters);
+    if (allocated) {
+        bitmap_set(iscsilun->allocmap,
+                   sector_num / iscsilun->cluster_sectors,
+                   DIV_ROUND_UP(nb_sectors, iscsilun->cluster_sectors));
+    } else if (nb_clusters > 0) {
+        bitmap_clear(iscsilun->allocmap, cluster_num, nb_clusters);
+    }
+
+    if (iscsilun->allocmap_valid == NULL) {
+        return;
+    }
+    if (valid) {
+        if (nb_clusters > 0) {
+            bitmap_set(iscsilun->allocmap_valid, cluster_num, nb_clusters);
+        }
+    } else {
+        bitmap_clear(iscsilun->allocmap_valid,
+                     sector_num / iscsilun->cluster_sectors,
+                     DIV_ROUND_UP(nb_sectors, iscsilun->cluster_sectors));
+    }
+}
+
+static void
+iscsi_allocmap_set_allocated(IscsiLun *iscsilun, int64_t sector_num,
+                             int nb_sectors)
+{
+    iscsi_allocmap_update(iscsilun, sector_num, nb_sectors, true, true);
+}
+
+static void
+iscsi_allocmap_set_unallocated(IscsiLun *iscsilun, int64_t sector_num,
+                               int nb_sectors)
+{
+    /* Note: if cache.direct=on the third argument to iscsi_allocmap_update
+     * is ignored, so this will in effect be an iscsi_allocmap_set_invalid.
+     */
+    iscsi_allocmap_update(iscsilun, sector_num, nb_sectors, false, true);
+}
+
+static void iscsi_allocmap_set_invalid(IscsiLun *iscsilun, int64_t sector_num,
+                                       int nb_sectors)
+{
+    iscsi_allocmap_update(iscsilun, sector_num, nb_sectors, false, false);
+}
+
+static void iscsi_allocmap_invalidate(IscsiLun *iscsilun)
+{
+    if (iscsilun->allocmap) {
+        bitmap_zero(iscsilun->allocmap, iscsilun->allocmap_size);
     }
+    if (iscsilun->allocmap_valid) {
+        bitmap_zero(iscsilun->allocmap_valid, iscsilun->allocmap_size);
+    }
+}
+
+static inline bool
+iscsi_allocmap_is_allocated(IscsiLun *iscsilun, int64_t sector_num,
+                            int nb_sectors)
+{
+    unsigned long size;
+    if (iscsilun->allocmap == NULL) {
+        return true;
+    }
+    size = DIV_ROUND_UP(sector_num + nb_sectors, iscsilun->cluster_sectors);
+    return !(find_next_bit(iscsilun->allocmap, size,
+                           sector_num / iscsilun->cluster_sectors) == size);
+}
+
+static inline bool iscsi_allocmap_is_valid(IscsiLun *iscsilun,
+                                           int64_t sector_num, int nb_sectors)
+{
+    unsigned long size;
+    if (iscsilun->allocmap_valid == NULL) {
+        return false;
+    }
+    size = DIV_ROUND_UP(sector_num + nb_sectors, iscsilun->cluster_sectors);
+    return (find_next_zero_bit(iscsilun->allocmap_valid, size,
+                               sector_num / iscsilun->cluster_sectors) == size);
 }
 
 static int coroutine_fn
@@ -515,26 +629,16 @@ retry:
     }
 
     if (iTask.status != SCSI_STATUS_GOOD) {
+        iscsi_allocmap_set_invalid(iscsilun, sector_num, nb_sectors);
         return iTask.err_code;
     }
 
-    iscsi_allocationmap_set(iscsilun, sector_num, nb_sectors);
+    iscsi_allocmap_set_allocated(iscsilun, sector_num, nb_sectors);
 
     return 0;
 }
 
 
-static bool iscsi_allocationmap_is_allocated(IscsiLun *iscsilun,
-                                             int64_t sector_num, int nb_sectors)
-{
-    unsigned long size;
-    if (iscsilun->allocationmap == NULL) {
-        return true;
-    }
-    size = DIV_ROUND_UP(sector_num + nb_sectors, iscsilun->cluster_sectors);
-    return !(find_next_bit(iscsilun->allocationmap, size,
-                           sector_num / iscsilun->cluster_sectors) == size);
-}
 
 static int64_t coroutine_fn iscsi_co_get_block_status(BlockDriverState *bs,
                                                   int64_t sector_num,
@@ -619,9 +723,9 @@ retry:
     }
 
     if (ret & BDRV_BLOCK_ZERO) {
-        iscsi_allocationmap_clear(iscsilun, sector_num, *pnum);
+        iscsi_allocmap_set_unallocated(iscsilun, sector_num, *pnum);
     } else {
-        iscsi_allocationmap_set(iscsilun, sector_num, *pnum);
+        iscsi_allocmap_set_allocated(iscsilun, sector_num, *pnum);
     }
 
     if (*pnum > nb_sectors) {
@@ -656,17 +760,32 @@ static int coroutine_fn iscsi_co_readv(BlockDriverState *bs,
         return -EINVAL;
     }
 
-    if (iscsilun->lbprz && nb_sectors >= ISCSI_CHECKALLOC_THRES &&
-        !iscsi_allocationmap_is_allocated(iscsilun, sector_num, nb_sectors)) {
-        int64_t ret;
+    /* if cache.direct is off and we have a valid entry in our allocation map
+     * we can skip checking the block status and directly return zeroes if
+     * the request falls within an unallocated area */
+    if (iscsi_allocmap_is_valid(iscsilun, sector_num, nb_sectors) &&
+        !iscsi_allocmap_is_allocated(iscsilun, sector_num, nb_sectors)) {
+            qemu_iovec_memset(iov, 0, 0x00, iov->size);
+            return 0;
+    }
+
+    if (nb_sectors >= ISCSI_CHECKALLOC_THRES &&
+        !iscsi_allocmap_is_valid(iscsilun, sector_num, nb_sectors) &&
+        !iscsi_allocmap_is_allocated(iscsilun, sector_num, nb_sectors)) {
         int pnum;
         BlockDriverState *file;
-        ret = iscsi_co_get_block_status(bs, sector_num,
-                                        BDRV_REQUEST_MAX_SECTORS, &pnum, &file);
+        /* check the block status from the beginning of the cluster
+         * containing the start sector */
+        int64_t ret = iscsi_co_get_block_status(bs,
+                          sector_num - sector_num % iscsilun->cluster_sectors,
+                          BDRV_REQUEST_MAX_SECTORS, &pnum, &file);
         if (ret < 0) {
             return ret;
         }
-        if (ret & BDRV_BLOCK_ZERO && pnum >= nb_sectors) {
+        /* if the whole request falls into an unallocated area we can avoid
+         * to read and directly return zeroes instead */
+        if (ret & BDRV_BLOCK_ZERO &&
+            pnum >= nb_sectors + sector_num % iscsilun->cluster_sectors) {
             qemu_iovec_memset(iov, 0, 0x00, iov->size);
             return 0;
         }
@@ -980,7 +1099,7 @@ retry:
         return iTask.err_code;
     }
 
-    iscsi_allocationmap_clear(iscsilun, sector_num, nb_sectors);
+    iscsi_allocmap_set_invalid(iscsilun, sector_num, nb_sectors);
 
     return 0;
 }
@@ -1070,15 +1189,17 @@ retry:
     }
 
     if (iTask.status != SCSI_STATUS_GOOD) {
+        iscsi_allocmap_set_invalid(iscsilun, offset >> BDRV_SECTOR_BITS,
+                                   count >> BDRV_SECTOR_BITS);
         return iTask.err_code;
     }
 
     if (flags & BDRV_REQ_MAY_UNMAP) {
-        iscsi_allocationmap_clear(iscsilun, offset >> BDRV_SECTOR_BITS,
-                                  count >> BDRV_SECTOR_BITS);
+        iscsi_allocmap_set_invalid(iscsilun, offset >> BDRV_SECTOR_BITS,
+                                   count >> BDRV_SECTOR_BITS);
     } else {
-        iscsi_allocationmap_set(iscsilun, offset >> BDRV_SECTOR_BITS,
-                                count >> BDRV_SECTOR_BITS);
+        iscsi_allocmap_set_allocated(iscsilun, offset >> BDRV_SECTOR_BITS,
+                                     count >> BDRV_SECTOR_BITS);
     }
 
     return 0;
@@ -1652,10 +1773,7 @@ static int iscsi_open(BlockDriverState *bs, QDict *options, int flags,
         iscsilun->cluster_sectors = (iscsilun->bl.opt_unmap_gran *
                                      iscsilun->block_size) >> BDRV_SECTOR_BITS;
         if (iscsilun->lbprz) {
-            iscsilun->allocationmap = iscsi_allocationmap_init(iscsilun);
-            if (iscsilun->allocationmap == NULL) {
-                ret = -ENOMEM;
-            }
+            ret = iscsi_allocmap_init(iscsilun, bs->open_flags);
         }
     }
 
@@ -1692,7 +1810,7 @@ static void iscsi_close(BlockDriverState *bs)
     }
     iscsi_destroy_context(iscsi);
     g_free(iscsilun->zeroblock);
-    g_free(iscsilun->allocationmap);
+    iscsi_allocmap_free(iscsilun);
     memset(iscsilun, 0, sizeof(IscsiLun));
 }
 
@@ -1754,6 +1872,16 @@ static int iscsi_reopen_prepare(BDRVReopenState *state,
     return 0;
 }
 
+static void iscsi_reopen_commit(BDRVReopenState *reopen_state)
+{
+    IscsiLun *iscsilun = reopen_state->bs->opaque;
+
+    /* the cache.direct status might have changed */
+    if (iscsilun->allocmap != NULL) {
+        iscsi_allocmap_init(iscsilun, reopen_state->flags);
+    }
+}
+
 static int iscsi_truncate(BlockDriverState *bs, int64_t offset)
 {
     IscsiLun *iscsilun = bs->opaque;
@@ -1773,9 +1901,8 @@ static int iscsi_truncate(BlockDriverState *bs, int64_t offset)
         return -EINVAL;
     }
 
-    if (iscsilun->allocationmap != NULL) {
-        g_free(iscsilun->allocationmap);
-        iscsilun->allocationmap = iscsi_allocationmap_init(iscsilun);
+    if (iscsilun->allocmap != NULL) {
+        iscsi_allocmap_init(iscsilun, bs->open_flags);
     }
 
     return 0;
@@ -1835,6 +1962,13 @@ static int iscsi_get_info(BlockDriverState *bs, BlockDriverInfo *bdi)
     return 0;
 }
 
+static void iscsi_invalidate_cache(BlockDriverState *bs,
+                                   Error **errp)
+{
+    IscsiLun *iscsilun = bs->opaque;
+    iscsi_allocmap_invalidate(iscsilun);
+}
+
 static QemuOptsList iscsi_create_opts = {
     .name = "iscsi-create-opts",
     .head = QTAILQ_HEAD_INITIALIZER(iscsi_create_opts.head),
@@ -1858,7 +1992,9 @@ static BlockDriver bdrv_iscsi = {
     .bdrv_close      = iscsi_close,
     .bdrv_create     = iscsi_create,
     .create_opts     = &iscsi_create_opts,
-    .bdrv_reopen_prepare  = iscsi_reopen_prepare,
+    .bdrv_reopen_prepare   = iscsi_reopen_prepare,
+    .bdrv_reopen_commit    = iscsi_reopen_commit,
+    .bdrv_invalidate_cache = iscsi_invalidate_cache,
 
     .bdrv_getlength  = iscsi_getlength,
     .bdrv_get_info   = iscsi_get_info,
-- 
1.9.1

Re: [Qemu-devel] [PATCH V4] block/iscsi: allow caching of the allocation map

[Paolo Bonzini]

On 30/06/2016 13:07, Peter Lieven wrote:
> +static void
> +iscsi_allocmap_update(IscsiLun *iscsilun, int64_t sector_num,
> +                      int nb_sectors, bool allocated, bool valid)
>  {
>      int64_t cluster_num, nb_clusters;
> -    if (iscsilun->allocationmap == NULL) {
> +
> +    if (iscsilun->allocmap == NULL) {
>          return;
>      }
>      cluster_num = DIV_ROUND_UP(sector_num, iscsilun->cluster_sectors);
>      nb_clusters = (sector_num + nb_sectors) / iscsilun->cluster_sectors
>                    - cluster_num;
> -    if (nb_clusters > 0) {
> -        bitmap_clear(iscsilun->allocationmap, cluster_num, nb_clusters);
> +    if (allocated) {
> +        bitmap_set(iscsilun->allocmap,
> +                   sector_num / iscsilun->cluster_sectors,
> +                   DIV_ROUND_UP(nb_sectors, iscsilun->cluster_sectors));
> +    } else if (nb_clusters > 0) {
> +        bitmap_clear(iscsilun->allocmap, cluster_num, nb_clusters);

I'm sorry for the delay in review, but this is still wrong.

Suppose cluster_sectors is 2, sector_num = 1, nb_sectors = 6:

   0--.--2--.--4--.--6--.--8
      |_________________|

Here in the "mark unallocated" case you want to set 2..6, i.e.
cluster_num=2, nb_clusters=2.  This is right.

   0--.--2--.--4--.--6--.--8
      xxx|___________|xxx     (x = shrunk)

In the "mark allocated" case, instead, you want to set 0..8, i.e.
cluster_num=0, nb_clusters=4.

   0--.--2--.--4--.--6--.--8
   <--|_________________|-->  (<--> = expanded)

  Instead you are setting nb_clusters=3, so that 6..8 is not marked
allocated and reading 6..7 will return zeroes:

   0--.--2--.--4--.--6--.--8
   <--|______________|!!!     (! = wrong)

 Instead you need to use

   DIV_ROUND_UP(sector_num + nb_sectors, ...)
       - sector_num / iscsilun->cluster_sectors

which does the rounding correctly.

In addition, there is some code duplication so put these computations in
two variables.

Thanks!

Paolo

> +    }
> +
> +    if (iscsilun->allocmap_valid == NULL) {
> +        return;
> +    }
> +    if (valid) {
> +        if (nb_clusters > 0) {
> +            bitmap_set(iscsilun->allocmap_valid, cluster_num, nb_clusters);
> +        }
> +    } else {
> +        bitmap_clear(iscsilun->allocmap_valid,
> +                     sector_num / iscsilun->cluster_sectors,
> +                     DIV_ROUND_UP(nb_sectors, iscsilun->cluster_sectors));
> +    }

Re: [Qemu-devel] [PATCH V4] block/iscsi: allow caching of the allocation map

[Peter Lieven]

Am 16.07.2016 um 15:38 schrieb Paolo Bonzini:
>
> On 30/06/2016 13:07, Peter Lieven wrote:
>> +static void
>> +iscsi_allocmap_update(IscsiLun *iscsilun, int64_t sector_num,
>> +                      int nb_sectors, bool allocated, bool valid)
>>   {
>>       int64_t cluster_num, nb_clusters;
>> -    if (iscsilun->allocationmap == NULL) {
>> +
>> +    if (iscsilun->allocmap == NULL) {
>>           return;
>>       }
>>       cluster_num = DIV_ROUND_UP(sector_num, iscsilun->cluster_sectors);
>>       nb_clusters = (sector_num + nb_sectors) / iscsilun->cluster_sectors
>>                     - cluster_num;
>> -    if (nb_clusters > 0) {
>> -        bitmap_clear(iscsilun->allocationmap, cluster_num, nb_clusters);
>> +    if (allocated) {
>> +        bitmap_set(iscsilun->allocmap,
>> +                   sector_num / iscsilun->cluster_sectors,
>> +                   DIV_ROUND_UP(nb_sectors, iscsilun->cluster_sectors));
>> +    } else if (nb_clusters > 0) {
>> +        bitmap_clear(iscsilun->allocmap, cluster_num, nb_clusters);
> I'm sorry for the delay in review, but this is still wrong.
>
> Suppose cluster_sectors is 2, sector_num = 1, nb_sectors = 6:
>
>     0--.--2--.--4--.--6--.--8
>        |_________________|
>
> Here in the "mark unallocated" case you want to set 2..6, i.e.
> cluster_num=2, nb_clusters=2.  This is right.
>
>     0--.--2--.--4--.--6--.--8
>        xxx|___________|xxx     (x = shrunk)

cluster_num = 1 and nb_clusters = 2

>
> In the "mark allocated" case, instead, you want to set 0..8, i.e.
> cluster_num=0, nb_clusters=4.
>
>     0--.--2--.--4--.--6--.--8
>     <--|_________________|-->  (<--> = expanded)
>
>    Instead you are setting nb_clusters=3, so that 6..8 is not marked
> allocated and reading 6..7 will return zeroes:
>
>     0--.--2--.--4--.--6--.--8
>     <--|______________|!!!     (! = wrong)
>
>   Instead you need to use
>
>     DIV_ROUND_UP(sector_num + nb_sectors, ...)
>         - sector_num / iscsilun->cluster_sectors
>
> which does the rounding correctly.

Right, but this has been wrong even in the currently active version.

So I would propose to send 2 patches.

1) fix the rounding in the old version cc'ing qemu-stable
2) rebase the new patch on top of that.

Thanks for catching this,
Peter

Re: [Qemu-devel] [PATCH V4] block/iscsi: allow caching of the allocation map

[Paolo Bonzini]

On 18/07/2016 09:55, Peter Lieven wrote:
> Am 16.07.2016 um 15:38 schrieb Paolo Bonzini:
>>
>> On 30/06/2016 13:07, Peter Lieven wrote:
>>> +static void
>>> +iscsi_allocmap_update(IscsiLun *iscsilun, int64_t sector_num,
>>> +                      int nb_sectors, bool allocated, bool valid)
>>>   {
>>>       int64_t cluster_num, nb_clusters;
>>> -    if (iscsilun->allocationmap == NULL) {
>>> +
>>> +    if (iscsilun->allocmap == NULL) {
>>>           return;
>>>       }
>>>       cluster_num = DIV_ROUND_UP(sector_num, iscsilun->cluster_sectors);
>>>       nb_clusters = (sector_num + nb_sectors) /
>>> iscsilun->cluster_sectors
>>>                     - cluster_num;
>>> -    if (nb_clusters > 0) {
>>> -        bitmap_clear(iscsilun->allocationmap, cluster_num,
>>> nb_clusters);
>>> +    if (allocated) {
>>> +        bitmap_set(iscsilun->allocmap,
>>> +                   sector_num / iscsilun->cluster_sectors,
>>> +                   DIV_ROUND_UP(nb_sectors,
>>> iscsilun->cluster_sectors));
>>> +    } else if (nb_clusters > 0) {
>>> +        bitmap_clear(iscsilun->allocmap, cluster_num, nb_clusters);
>> I'm sorry for the delay in review, but this is still wrong.
>>
>> Suppose cluster_sectors is 2, sector_num = 1, nb_sectors = 6:
>>
>>     0--.--2--.--4--.--6--.--8
>>        |_________________|
>>
>> Here in the "mark unallocated" case you want to set 2..6, i.e.
>> cluster_num=2, nb_clusters=2.  This is right.
>>
>>     0--.--2--.--4--.--6--.--8
>>        xxx|___________|xxx     (x = shrunk)
> 
> cluster_num = 1 and nb_clusters = 2
> 
>>
>> In the "mark allocated" case, instead, you want to set 0..8, i.e.
>> cluster_num=0, nb_clusters=4.
>>
>>     0--.--2--.--4--.--6--.--8
>>     <--|_________________|-->  (<--> = expanded)
>>
>>    Instead you are setting nb_clusters=3, so that 6..8 is not marked
>> allocated and reading 6..7 will return zeroes:
>>
>>     0--.--2--.--4--.--6--.--8
>>     <--|______________|!!!     (! = wrong)
>>
>>   Instead you need to use
>>
>>     DIV_ROUND_UP(sector_num + nb_sectors, ...)
>>         - sector_num / iscsilun->cluster_sectors
>>
>> which does the rounding correctly.
> 
> Right, but this has been wrong even in the currently active version.
> 
> So I would propose to send 2 patches.
> 
> 1) fix the rounding in the old version cc'ing qemu-stable
> 2) rebase the new patch on top of that.

That's okay.

Paolo