[v2] Add subcluster allocation to qcow2

[RFC PATCH v2 10/26] qcow2: Update get/set_l2_entry() and add get/set_l2_bitmap()

Posted by Alberto Garcia 6 years, 3 months ago

Extended L2 entries are 128-bit wide: 64 bits for the entry itself and
64 bits for the subcluster allocation bitmap.

In order to support them correctly get/set_l2_entry() need to be
updated so they take the entry width into account in order to
calculate the correct offset.

This patch also adds the get/set_l2_bitmap() functions that are used
to access the bitmaps. For convenience, these functions are no-ops
when used in traditional qcow2 images.

Signed-off-by: Alberto Garcia <berto@igalia.com>
---
 block/qcow2.h | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/block/qcow2.h b/block/qcow2.h
index 29a253bfb9..741c41c80f 100644
--- a/block/qcow2.h
+++ b/block/qcow2.h
@@ -507,15 +507,37 @@ static inline size_t l2_entry_size(BDRVQcow2State *s)
 static inline uint64_t get_l2_entry(BDRVQcow2State *s, uint64_t *l2_slice,
                                     int idx)
 {
+    idx *= l2_entry_size(s) / sizeof(uint64_t);
     return be64_to_cpu(l2_slice[idx]);
 }
 
+static inline uint64_t get_l2_bitmap(BDRVQcow2State *s, uint64_t *l2_slice,
+                                     int idx)
+{
+    if (has_subclusters(s)) {
+        idx *= l2_entry_size(s) / sizeof(uint64_t);
+        return be64_to_cpu(l2_slice[idx + 1]);
+    } else {
+        return 0;
+    }
+}
+
 static inline void set_l2_entry(BDRVQcow2State *s, uint64_t *l2_slice,
                                 int idx, uint64_t entry)
 {
+    idx *= l2_entry_size(s) / sizeof(uint64_t);
     l2_slice[idx] = cpu_to_be64(entry);
 }
 
+static inline void set_l2_bitmap(BDRVQcow2State *s, uint64_t *l2_slice,
+                                 int idx, uint64_t bitmap)
+{
+    if (has_subclusters(s)) {
+        idx *= l2_entry_size(s) / sizeof(uint64_t);
+        l2_slice[idx + 1] = cpu_to_be64(bitmap);
+    }
+}
+
 static inline bool has_data_file(BlockDriverState *bs)
 {
     BDRVQcow2State *s = bs->opaque;
-- 
2.20.1

Re: [RFC PATCH v2 10/26] qcow2: Update get/set_l2_entry() and add get/set_l2_bitmap()

Posted by Max Reitz 6 years, 3 months ago

On 26.10.19 23:25, Alberto Garcia wrote:
> Extended L2 entries are 128-bit wide: 64 bits for the entry itself and
> 64 bits for the subcluster allocation bitmap.
> 
> In order to support them correctly get/set_l2_entry() need to be
> updated so they take the entry width into account in order to
> calculate the correct offset.
> 
> This patch also adds the get/set_l2_bitmap() functions that are used
> to access the bitmaps. For convenience, these functions are no-ops
> when used in traditional qcow2 images.

Granted, I haven’t seen the following patches yet, but if these
functions are indeed called for images that don’t have subclusters,
shouldn’t they return 0x0*0f*f then? (i.e. everything allocated)

If they aren’t, they should probably just abort().  Well,
set_l2_bitmap() should probably always abort() if there aren’t any
subclusters.

Max

> Signed-off-by: Alberto Garcia <berto@igalia.com>
> ---
>  block/qcow2.h | 22 ++++++++++++++++++++++
>  1 file changed, 22 insertions(+)
> 
> diff --git a/block/qcow2.h b/block/qcow2.h
> index 29a253bfb9..741c41c80f 100644
> --- a/block/qcow2.h
> +++ b/block/qcow2.h
> @@ -507,15 +507,37 @@ static inline size_t l2_entry_size(BDRVQcow2State *s)
>  static inline uint64_t get_l2_entry(BDRVQcow2State *s, uint64_t *l2_slice,
>                                      int idx)
>  {
> +    idx *= l2_entry_size(s) / sizeof(uint64_t);
>      return be64_to_cpu(l2_slice[idx]);
>  }
>  
> +static inline uint64_t get_l2_bitmap(BDRVQcow2State *s, uint64_t *l2_slice,
> +                                     int idx)
> +{
> +    if (has_subclusters(s)) {
> +        idx *= l2_entry_size(s) / sizeof(uint64_t);
> +        return be64_to_cpu(l2_slice[idx + 1]);
> +    } else {
> +        return 0;
> +    }
> +}
> +
>  static inline void set_l2_entry(BDRVQcow2State *s, uint64_t *l2_slice,
>                                  int idx, uint64_t entry)
>  {
> +    idx *= l2_entry_size(s) / sizeof(uint64_t);
>      l2_slice[idx] = cpu_to_be64(entry);
>  }
>  
> +static inline void set_l2_bitmap(BDRVQcow2State *s, uint64_t *l2_slice,
> +                                 int idx, uint64_t bitmap)
> +{
> +    if (has_subclusters(s)) {
> +        idx *= l2_entry_size(s) / sizeof(uint64_t);
> +        l2_slice[idx + 1] = cpu_to_be64(bitmap);
> +    }
> +}
> +
>  static inline bool has_data_file(BlockDriverState *bs)
>  {
>      BDRVQcow2State *s = bs->opaque;
>

Re: [RFC PATCH v2 10/26] qcow2: Update get/set_l2_entry() and add get/set_l2_bitmap()

Posted by Alberto Garcia 6 years, 2 months ago

On Wed 30 Oct 2019 05:55:04 PM CET, Max Reitz wrote:
>> This patch also adds the get/set_l2_bitmap() functions that are used
>> to access the bitmaps. For convenience, these functions are no-ops
>> when used in traditional qcow2 images.
>
> Granted, I haven’t seen the following patches yet, but if these
> functions are indeed called for images that don’t have subclusters,
> shouldn’t they return 0x0*0f*f then? (i.e. everything allocated)
>
> If they aren’t, they should probably just abort().  Well,
> set_l2_bitmap() should probably always abort() if there aren’t any
> subclusters.

Yeah, set_l2_bitmap() should abort (I had this changed already).

About get_l2_bitmap() ... I decided not to abort for convenience, for
cases like this one:

    uint64_t l2_entry = get_l2_entry(s, l2_slice, l2_index);
    uint64_t l2_bitmap = get_l2_bitmap(s, l2_slice, l2_index);
    type = qcow2_get_subcluster_type(bs, l2_entry, l2_bitmap, sc);

Here the value of l2_bitmap is going to be ignored anyway so it doesn't
matter what we return, but perhaps for consistency we should return
QCOW_OFLAG_SUB_ALLOC(0), which means that the first (and only, in this
case) subcluster is allocated.

Berto