[Qemu-devel] [PATCH] qcow2: Replace align_offset() with ROUND_UP()

[Qemu-devel] [PATCH] qcow2: Replace align_offset() with ROUND_UP()

[Alberto Garcia]

The align_offset() function is equivalent to the ROUND_UP() macro so
there's no need to use the former. The ROUND_UP() name is also a bit
more explicit.

This patch uses ROUND_UP() instead of the slower QEMU_ALIGN_UP()
because align_offset() already requires that the second parameter is a
power of two.

Signed-off-by: Alberto Garcia <berto@igalia.com>
---
 block/qcow2-bitmap.c   |  2 +-
 block/qcow2-cluster.c  |  4 ++--
 block/qcow2-refcount.c |  4 ++--
 block/qcow2-snapshot.c | 10 +++++-----
 block/qcow2.c          | 12 ++++++------
 block/qcow2.h          |  6 ------
 6 files changed, 16 insertions(+), 22 deletions(-)

diff --git a/block/qcow2-bitmap.c b/block/qcow2-bitmap.c
index efa10c6663..1cf99ca51e 100644
--- a/block/qcow2-bitmap.c
+++ b/block/qcow2-bitmap.c
@@ -413,7 +413,7 @@ static inline void bitmap_dir_entry_to_be(Qcow2BitmapDirEntry *entry)
 
 static inline int calc_dir_entry_size(size_t name_size, size_t extra_data_size)
 {
-    return align_offset(sizeof(Qcow2BitmapDirEntry) +
+    return ROUND_UP(sizeof(Qcow2BitmapDirEntry) +
                         name_size + extra_data_size, 8);
 }
 
diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
index a3fec27bf9..29d70e1f3e 100644
--- a/block/qcow2-cluster.c
+++ b/block/qcow2-cluster.c
@@ -127,11 +127,11 @@ int qcow2_grow_l1_table(BlockDriverState *bs, uint64_t min_size,
 
     new_l1_size2 = sizeof(uint64_t) * new_l1_size;
     new_l1_table = qemu_try_blockalign(bs->file->bs,
-                                       align_offset(new_l1_size2, 512));
+                                       ROUND_UP(new_l1_size2, 512));
     if (new_l1_table == NULL) {
         return -ENOMEM;
     }
-    memset(new_l1_table, 0, align_offset(new_l1_size2, 512));
+    memset(new_l1_table, 0, ROUND_UP(new_l1_size2, 512));
 
     if (s->l1_size) {
         memcpy(new_l1_table, s->l1_table, s->l1_size * sizeof(uint64_t));
diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c
index 92701ab7af..1d520615a8 100644
--- a/block/qcow2-refcount.c
+++ b/block/qcow2-refcount.c
@@ -1202,7 +1202,7 @@ int qcow2_update_snapshot_refcount(BlockDriverState *bs,
      * l1_table_offset when it is the current s->l1_table_offset! Be careful
      * when changing this! */
     if (l1_table_offset != s->l1_table_offset) {
-        l1_table = g_try_malloc0(align_offset(l1_size2, 512));
+        l1_table = g_try_malloc0(ROUND_UP(l1_size2, 512));
         if (l1_size2 && l1_table == NULL) {
             ret = -ENOMEM;
             goto fail;
@@ -2545,7 +2545,7 @@ int qcow2_check_metadata_overlap(BlockDriverState *bs, int ign, int64_t offset,
     }
 
     /* align range to test to cluster boundaries */
-    size = align_offset(offset_into_cluster(s, offset) + size, s->cluster_size);
+    size = ROUND_UP(offset_into_cluster(s, offset) + size, s->cluster_size);
     offset = start_of_cluster(s, offset);
 
     if ((chk & QCOW2_OL_ACTIVE_L1) && s->l1_size) {
diff --git a/block/qcow2-snapshot.c b/block/qcow2-snapshot.c
index 44243e0e95..cee25f582b 100644
--- a/block/qcow2-snapshot.c
+++ b/block/qcow2-snapshot.c
@@ -66,7 +66,7 @@ int qcow2_read_snapshots(BlockDriverState *bs)
 
     for(i = 0; i < s->nb_snapshots; i++) {
         /* Read statically sized part of the snapshot header */
-        offset = align_offset(offset, 8);
+        offset = ROUND_UP(offset, 8);
         ret = bdrv_pread(bs->file, offset, &h, sizeof(h));
         if (ret < 0) {
             goto fail;
@@ -155,7 +155,7 @@ static int qcow2_write_snapshots(BlockDriverState *bs)
     offset = 0;
     for(i = 0; i < s->nb_snapshots; i++) {
         sn = s->snapshots + i;
-        offset = align_offset(offset, 8);
+        offset = ROUND_UP(offset, 8);
         offset += sizeof(h);
         offset += sizeof(extra);
         offset += strlen(sn->id_str);
@@ -215,7 +215,7 @@ static int qcow2_write_snapshots(BlockDriverState *bs)
         assert(id_str_size <= UINT16_MAX && name_size <= UINT16_MAX);
         h.id_str_size = cpu_to_be16(id_str_size);
         h.name_size = cpu_to_be16(name_size);
-        offset = align_offset(offset, 8);
+        offset = ROUND_UP(offset, 8);
 
         ret = bdrv_pwrite(bs->file, offset, &h, sizeof(h));
         if (ret < 0) {
@@ -441,7 +441,7 @@ int qcow2_snapshot_create(BlockDriverState *bs, QEMUSnapshotInfo *sn_info)
     /* The VM state isn't needed any more in the active L1 table; in fact, it
      * hurts by causing expensive COW for the next snapshot. */
     qcow2_cluster_discard(bs, qcow2_vm_state_offset(s),
-                          align_offset(sn->vm_state_size, s->cluster_size),
+                          ROUND_UP(sn->vm_state_size, s->cluster_size),
                           QCOW2_DISCARD_NEVER, false);
 
 #ifdef DEBUG_ALLOC
@@ -710,7 +710,7 @@ int qcow2_snapshot_load_tmp(BlockDriverState *bs,
     }
     new_l1_bytes = sn->l1_size * sizeof(uint64_t);
     new_l1_table = qemu_try_blockalign(bs->file->bs,
-                                       align_offset(new_l1_bytes, 512));
+                                       ROUND_UP(new_l1_bytes, 512));
     if (new_l1_table == NULL) {
         return -ENOMEM;
     }
diff --git a/block/qcow2.c b/block/qcow2.c
index 1f80961e1b..e09d5c2a74 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -1354,7 +1354,7 @@ static int qcow2_do_open(BlockDriverState *bs, QDict *options, int flags,
 
     if (s->l1_size > 0) {
         s->l1_table = qemu_try_blockalign(bs->file->bs,
-            align_offset(s->l1_size * sizeof(uint64_t), 512));
+            ROUND_UP(s->l1_size * sizeof(uint64_t), 512));
         if (s->l1_table == NULL) {
             error_setg(errp, "Could not allocate L1 table");
             ret = -ENOMEM;
@@ -2615,19 +2615,19 @@ static int64_t qcow2_calc_prealloc_size(int64_t total_size,
 {
     int64_t meta_size = 0;
     uint64_t nl1e, nl2e;
-    int64_t aligned_total_size = align_offset(total_size, cluster_size);
+    int64_t aligned_total_size = ROUND_UP(total_size, cluster_size);
 
     /* header: 1 cluster */
     meta_size += cluster_size;
 
     /* total size of L2 tables */
     nl2e = aligned_total_size / cluster_size;
-    nl2e = align_offset(nl2e, cluster_size / sizeof(uint64_t));
+    nl2e = ROUND_UP(nl2e, cluster_size / sizeof(uint64_t));
     meta_size += nl2e * sizeof(uint64_t);
 
     /* total size of L1 tables */
     nl1e = nl2e * sizeof(uint64_t) / cluster_size;
-    nl1e = align_offset(nl1e, cluster_size / sizeof(uint64_t));
+    nl1e = ROUND_UP(nl1e, cluster_size / sizeof(uint64_t));
     meta_size += nl1e * sizeof(uint64_t);
 
     /* total size of refcount table and blocks */
@@ -3681,7 +3681,7 @@ static BlockMeasureInfo *qcow2_measure(QemuOpts *opts, BlockDriverState *in_bs,
     has_backing_file = !!optstr;
     g_free(optstr);
 
-    virtual_size = align_offset(qemu_opt_get_size_del(opts, BLOCK_OPT_SIZE, 0),
+    virtual_size = ROUND_UP(qemu_opt_get_size_del(opts, BLOCK_OPT_SIZE, 0),
                                 cluster_size);
 
     /* Check that virtual disk size is valid */
@@ -3702,7 +3702,7 @@ static BlockMeasureInfo *qcow2_measure(QemuOpts *opts, BlockDriverState *in_bs,
             goto err;
         }
 
-        virtual_size = align_offset(ssize, cluster_size);
+        virtual_size = ROUND_UP(ssize, cluster_size);
 
         if (has_backing_file) {
             /* We don't how much of the backing chain is shared by the input
diff --git a/block/qcow2.h b/block/qcow2.h
index 46c8cf44ec..33d2eb0ead 100644
--- a/block/qcow2.h
+++ b/block/qcow2.h
@@ -468,12 +468,6 @@ static inline int offset_to_l2_index(BDRVQcow2State *s, int64_t offset)
     return (offset >> s->cluster_bits) & (s->l2_size - 1);
 }
 
-static inline int64_t align_offset(int64_t offset, int n)
-{
-    offset = (offset + n - 1) & ~(n - 1);
-    return offset;
-}
-
 static inline int64_t qcow2_vm_state_offset(BDRVQcow2State *s)
 {
     return (int64_t)s->l1_vm_state_index << (s->cluster_bits + s->l2_bits);
-- 
2.11.0

Re: [Qemu-devel] [PATCH] qcow2: Replace align_offset() with ROUND_UP()

[Eric Blake]

[-- Attachment #1: Type: text/plain, Size: 1734 bytes --]

On 01/30/2018 09:04 AM, Alberto Garcia wrote:
> The align_offset() function is equivalent to the ROUND_UP() macro so
> there's no need to use the former. The ROUND_UP() name is also a bit
> more explicit.
> 
> This patch uses ROUND_UP() instead of the slower QEMU_ALIGN_UP()
> because align_offset() already requires that the second parameter is a
> power of two.

(Presumably, for the cases where the second argument is a compile-time
constant, the compiler emits the same code for either macro - but I
agree that QEMU_ALIGN_UP can be slower where the compiler can't see it
is a power of 2)

> 
> Signed-off-by: Alberto Garcia <berto@igalia.com>
> ---
> +++ b/block/qcow2-bitmap.c
> @@ -413,7 +413,7 @@ static inline void bitmap_dir_entry_to_be(Qcow2BitmapDirEntry *entry)
>  
>  static inline int calc_dir_entry_size(size_t name_size, size_t extra_data_size)
>  {
> -    return align_offset(sizeof(Qcow2BitmapDirEntry) +
> +    return ROUND_UP(sizeof(Qcow2BitmapDirEntry) +
>                          name_size + extra_data_size, 8);

Indentation alignment is now off.


> +++ b/block/qcow2.c

> @@ -3681,7 +3681,7 @@ static BlockMeasureInfo *qcow2_measure(QemuOpts *opts, BlockDriverState *in_bs,
>      has_backing_file = !!optstr;
>      g_free(optstr);
>  
> -    virtual_size = align_offset(qemu_opt_get_size_del(opts, BLOCK_OPT_SIZE, 0),
> +    virtual_size = ROUND_UP(qemu_opt_get_size_del(opts, BLOCK_OPT_SIZE, 0),
>                                  cluster_size);

and again.

With the whitespace fixed,
Reviewed-by: Eric Blake <eblake@redhat.com>

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org


[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 619 bytes --]

Re: [Qemu-devel] [PATCH] qcow2: Replace align_offset() with ROUND_UP()

[Alberto Garcia]

On Tue 30 Jan 2018 05:03:16 PM CET, Eric Blake wrote:

>> -    virtual_size = align_offset(qemu_opt_get_size_del(opts, BLOCK_OPT_SIZE, 0),
>> +    virtual_size = ROUND_UP(qemu_opt_get_size_del(opts, BLOCK_OPT_SIZE, 0),
>>                                  cluster_size);

I just realized that the first parameter here is a function call with
side effects, it it safe to use ROUND_UP() in this case?

#define ROUND_UP(n, d) (((n) + (d) - 1) & -(0 ? (n) : (d)))

Berto

Re: [Qemu-devel] [PATCH] qcow2: Replace align_offset() with ROUND_UP()

[Eric Blake]

[-- Attachment #1: Type: text/plain, Size: 851 bytes --]

On 01/30/2018 10:08 AM, Alberto Garcia wrote:
> On Tue 30 Jan 2018 05:03:16 PM CET, Eric Blake wrote:
> 
>>> -    virtual_size = align_offset(qemu_opt_get_size_del(opts, BLOCK_OPT_SIZE, 0),
>>> +    virtual_size = ROUND_UP(qemu_opt_get_size_del(opts, BLOCK_OPT_SIZE, 0),
>>>                                  cluster_size);
> 
> I just realized that the first parameter here is a function call with
> side effects, it it safe to use ROUND_UP() in this case?
> 
> #define ROUND_UP(n, d) (((n) + (d) - 1) & -(0 ? (n) : (d)))

Oh, good catch.  No, we need a temporary variable to hold the result of
the function call (or we could rewrite ROUND_UP to have evaluate-once
semantics using gcc/clang extensions).

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org


[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 619 bytes --]

Re: [Qemu-devel] [PATCH] qcow2: Replace align_offset() with ROUND_UP()

[Alberto Garcia]

On Tue 30 Jan 2018 05:17:47 PM CET, Eric Blake wrote:
> On 01/30/2018 10:08 AM, Alberto Garcia wrote:
>> On Tue 30 Jan 2018 05:03:16 PM CET, Eric Blake wrote:
>> 
>>>> -    virtual_size = align_offset(qemu_opt_get_size_del(opts, BLOCK_OPT_SIZE, 0),
>>>> +    virtual_size = ROUND_UP(qemu_opt_get_size_del(opts, BLOCK_OPT_SIZE, 0),
>>>>                                  cluster_size);
>> 
>> I just realized that the first parameter here is a function call with
>> side effects, it it safe to use ROUND_UP() in this case?
>> 
>> #define ROUND_UP(n, d) (((n) + (d) - 1) & -(0 ? (n) : (d)))
>
> Oh, good catch.  No, we need a temporary variable to hold the result
> of the function call

...which is what align_offset() was doing in the first place. I can
still modify that function to use the macro internally.

Berto

Re: [Qemu-devel] [PATCH] qcow2: Replace align_offset() with ROUND_UP()

[Eric Blake]

[-- Attachment #1: Type: text/plain, Size: 1330 bytes --]

On 01/30/2018 10:22 AM, Alberto Garcia wrote:
> On Tue 30 Jan 2018 05:17:47 PM CET, Eric Blake wrote:
>> On 01/30/2018 10:08 AM, Alberto Garcia wrote:
>>> On Tue 30 Jan 2018 05:03:16 PM CET, Eric Blake wrote:
>>>
>>>>> -    virtual_size = align_offset(qemu_opt_get_size_del(opts, BLOCK_OPT_SIZE, 0),
>>>>> +    virtual_size = ROUND_UP(qemu_opt_get_size_del(opts, BLOCK_OPT_SIZE, 0),
>>>>>                                  cluster_size);
>>>
>>> I just realized that the first parameter here is a function call with
>>> side effects, it it safe to use ROUND_UP() in this case?
>>>
>>> #define ROUND_UP(n, d) (((n) + (d) - 1) & -(0 ? (n) : (d)))
>>
>> Oh, good catch.  No, we need a temporary variable to hold the result
>> of the function call
> 
> ...which is what align_offset() was doing in the first place. I can
> still modify that function to use the macro internally.

Nah. I think the ROUND_UP naming is enough to remind us to be careful,
and since this was the only affected spot in your conversion, it's nicer
to drop align_offset() and just do:

virtual_size = qemu_opt_get_size_del(opts, BLOCK_OPT_SIZE, 0);
virtual_size = ROUND_UP(virtual_size, cluster_size);

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org


[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 619 bytes --]

Re: [Qemu-devel] [PATCH] qcow2: Replace align_offset() with ROUND_UP()

[Alberto Garcia]

On Tue 30 Jan 2018 05:17:47 PM CET, Eric Blake wrote:

>>>> -    virtual_size = align_offset(qemu_opt_get_size_del(opts, BLOCK_OPT_SIZE, 0),
>>>> +    virtual_size = ROUND_UP(qemu_opt_get_size_del(opts, BLOCK_OPT_SIZE, 0),
>>>>                                  cluster_size);
>> 
>> I just realized that the first parameter here is a function call with
>> side effects, it it safe to use ROUND_UP() in this case?
>> 
>> #define ROUND_UP(n, d) (((n) + (d) - 1) & -(0 ? (n) : (d)))
>
> Oh, good catch.  No, we need a temporary variable to hold the result
> of the function call (or we could rewrite ROUND_UP to have
> evaluate-once semantics using gcc/clang extensions).

It was actually not a problem since C guarantees that the (n) in the
conditional expression is only evaluated if the first operand is != 0.
So (n) is only evaluated once.

Anyway, I rewrote it in the new patch as you suggested since it looks a
bit more readable.

Berto