[Qemu-devel] [PATCH 0/3] block: byte-based blocking read/write

[Qemu-devel] [PATCH 0/3] block: byte-based blocking read/write

[Eric Blake]

A logical followup to my other recent cleanups.  The only remaining
mention of sectors in block.h APIs is in bdrv_nb_sectors()
(converting those callers to bdrv_getlength() not only requires more
work, but would be our opportunity to see if we could quit rounding
block sizes to sector boundaries for byte-based protocols that can
actually report an exact unaligned size) and for computing geometries
(where it actually makes sense).

Based-on: <20180424192506.149089-1-eblake@redhat.com>
([PATCH v2 0/6] block: byte-based AIO read/write)
Based-on: <20180426025129.621969-1-eblake@redhat.com>
([PATCH v6 0/6] minor qcow2 compression improvements)

Eric Blake (3):
  vdi: Switch to byte-based calls
  vvfat: Switch to byte-based calls
  block: Removed unused sector-based blocking I/O

 include/block/block.h |  4 ----
 block/io.c            | 48 ++++++++----------------------------------------
 block/vdi.c           | 14 +++++++-------
 block/vvfat.c         | 20 +++++++++++---------
 4 files changed, 26 insertions(+), 60 deletions(-)

-- 
2.14.3

[Qemu-devel] [PATCH 1/3] vdi: Switch to byte-based calls

[Eric Blake]

We are gradually moving away from sector-based interfaces, towards
byte-based.  Make the change for the last few sector-based calls
into the block layer from the vdi driver.

Ideally, the vdi driver should switch to doing everything
byte-based, but that's a more invasive change that requires a
bit more auditing.

Signed-off-by: Eric Blake <eblake@redhat.com>
---
 block/vdi.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/block/vdi.c b/block/vdi.c
index 4a2d1ff88d4..fd745982caf 100644
--- a/block/vdi.c
+++ b/block/vdi.c
@@ -379,7 +379,7 @@ static int vdi_open(BlockDriverState *bs, QDict *options, int flags,

     logout("\n");

-    ret = bdrv_read(bs->file, 0, (uint8_t *)&header, 1);
+    ret = bdrv_pread(bs->file, 0, &header, sizeof(header));
     if (ret < 0) {
         goto fail;
     }
@@ -468,15 +468,14 @@ static int vdi_open(BlockDriverState *bs, QDict *options, int flags,
     s->header = header;

     bmap_size = header.blocks_in_image * sizeof(uint32_t);
-    bmap_size = DIV_ROUND_UP(bmap_size, SECTOR_SIZE);
-    s->bmap = qemu_try_blockalign(bs->file->bs, bmap_size * SECTOR_SIZE);
+    s->bmap = qemu_try_blockalign(bs->file->bs, bmap_size);
     if (s->bmap == NULL) {
         ret = -ENOMEM;
         goto fail;
     }

-    ret = bdrv_read(bs->file, s->bmap_sector, (uint8_t *)s->bmap,
-                    bmap_size);
+    ret = bdrv_pread(bs->file, s->bmap_sector * SECTOR_SIZE, s->bmap,
+                     bmap_size);
     if (ret < 0) {
         goto fail_free_bmap;
     }
@@ -695,7 +694,7 @@ nonallocating_write:
         assert(VDI_IS_ALLOCATED(bmap_first));
         *header = s->header;
         vdi_header_to_le(header);
-        ret = bdrv_write(bs->file, 0, block, 1);
+        ret = bdrv_pwrite(bs->file, 0, block, SECTOR_SIZE);
         g_free(block);
         block = NULL;

@@ -713,7 +712,8 @@ nonallocating_write:
         base = ((uint8_t *)&s->bmap[0]) + bmap_first * SECTOR_SIZE;
         logout("will write %u block map sectors starting from entry %u\n",
                n_sectors, bmap_first);
-        ret = bdrv_write(bs->file, offset, base, n_sectors);
+        ret = bdrv_pwrite(bs->file, offset * SECTOR_SIZE, base,
+                          n_sectors * SECTOR_SIZE);
     }

     return ret;
-- 
2.14.3

[Qemu-devel] [PATCH 2/3] vvfat: Switch to byte-based calls

[Eric Blake]

We are gradually moving away from sector-based interfaces, towards
byte-based.  Make the change for the last few sector-based calls
into the block layer from the vvfat driver.

Ideally, the vvfat driver should switch to doing everything
byte-based, but that's a more invasive change that requires a
bit more auditing.

Signed-off-by: Eric Blake <eblake@redhat.com>
---
 block/vvfat.c | 20 +++++++++++---------
 1 file changed, 11 insertions(+), 9 deletions(-)

diff --git a/block/vvfat.c b/block/vvfat.c
index 1569783b0f9..ba27f86a951 100644
--- a/block/vvfat.c
+++ b/block/vvfat.c
@@ -1503,8 +1503,8 @@ static int vvfat_read(BlockDriverState *bs, int64_t sector_num,
                 DLOG(fprintf(stderr, "sectors %" PRId64 "+%" PRId64
                              " allocated\n", sector_num,
                              n >> BDRV_SECTOR_BITS));
-                if (bdrv_read(s->qcow, sector_num, buf + i * 0x200,
-                              n >> BDRV_SECTOR_BITS)) {
+                if (bdrv_pread(s->qcow, sector_num * BDRV_SECTOR_BITS,
+                               buf + i * 0x200, n) < 0) {
                     return -1;
                 }
                 i += (n >> BDRV_SECTOR_BITS) - 1;
@@ -1992,7 +1992,8 @@ static uint32_t get_cluster_count_for_direntry(BDRVVVFATState* s,
                         if (res) {
                             return -1;
                         }
-                        res = bdrv_write(s->qcow, offset, s->cluster_buffer, 1);
+                        res = bdrv_pwrite(s->qcow, offset * BDRV_SECTOR_SIZE,
+                                          s->cluster_buffer, BDRV_SECTOR_SIZE);
                         if (res) {
                             return -2;
                         }
@@ -2155,7 +2156,7 @@ DLOG(checkpoint());
      * - get modified FAT
      * - compare the two FATs (TODO)
      * - get buffer for marking used clusters
-     * - recurse direntries from root (using bs->bdrv_read to make
+     * - recurse direntries from root (using bs->bdrv_pread to make
      *    sure to get the new data)
      *   - check that the FAT agrees with the size
      *   - count the number of clusters occupied by this directory and
@@ -2902,9 +2903,9 @@ static int handle_deletes(BDRVVVFATState* s)
 /*
  * synchronize mapping with new state:
  *
- * - copy FAT (with bdrv_read)
+ * - copy FAT (with bdrv_pread)
  * - mark all filenames corresponding to mappings as deleted
- * - recurse direntries from root (using bs->bdrv_read)
+ * - recurse direntries from root (using bs->bdrv_pread)
  * - delete files corresponding to mappings marked as deleted
  */
 static int do_commit(BDRVVVFATState* s)
@@ -2924,10 +2925,10 @@ static int do_commit(BDRVVVFATState* s)
         return ret;
     }

-    /* copy FAT (with bdrv_read) */
+    /* copy FAT (with bdrv_pread) */
     memcpy(s->fat.pointer, s->fat2, 0x200 * s->sectors_per_fat);

-    /* recurse direntries from root (using bs->bdrv_read) */
+    /* recurse direntries from root (using bs->bdrv_pread) */
     ret = commit_direntries(s, 0, -1);
     if (ret) {
         fprintf(stderr, "Fatal: error while committing (%d)\n", ret);
@@ -3041,7 +3042,8 @@ DLOG(checkpoint());
      * Use qcow backend. Commit later.
      */
 DLOG(fprintf(stderr, "Write to qcow backend: %d + %d\n", (int)sector_num, nb_sectors));
-    ret = bdrv_write(s->qcow, sector_num, buf, nb_sectors);
+    ret = bdrv_pwrite(s->qcow, sector_num * BDRV_SECTOR_SIZE, buf,
+                      nb_sectors * BDRV_SECTOR_SIZE);
     if (ret < 0) {
         fprintf(stderr, "Error writing to qcow backend\n");
         return ret;
-- 
2.14.3

[Qemu-devel] [PATCH 3/3] block: Removed unused sector-based blocking I/O

[Eric Blake]

We are gradually moving away from sector-based interfaces, towards
byte-based.  Now that all callers of blocking I/O have been converted
to use our preferred byte-based bdrv_p{read,write}(), we can
delete the unused bdrv_{read,write}().

Signed-off-by: Eric Blake <eblake@redhat.com>
---
 include/block/block.h |  4 ----
 block/io.c            | 48 ++++++++----------------------------------------
 2 files changed, 8 insertions(+), 44 deletions(-)

diff --git a/include/block/block.h b/include/block/block.h
index 8b191c23d97..a355c2c5319 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -265,10 +265,6 @@ int bdrv_reopen_prepare(BDRVReopenState *reopen_state,
                         BlockReopenQueue *queue, Error **errp);
 void bdrv_reopen_commit(BDRVReopenState *reopen_state);
 void bdrv_reopen_abort(BDRVReopenState *reopen_state);
-int bdrv_read(BdrvChild *child, int64_t sector_num,
-              uint8_t *buf, int nb_sectors);
-int bdrv_write(BdrvChild *child, int64_t sector_num,
-               const uint8_t *buf, int nb_sectors);
 int bdrv_pwrite_zeroes(BdrvChild *child, int64_t offset,
                        int bytes, BdrvRequestFlags flags);
 int bdrv_make_zero(BdrvChild *child, BdrvRequestFlags flags);
diff --git a/block/io.c b/block/io.c
index 7155786eb47..f39d99ff210 100644
--- a/block/io.c
+++ b/block/io.c
@@ -715,45 +715,6 @@ static int bdrv_prwv_co(BdrvChild *child, int64_t offset,
     return rwco.ret;
 }

-/*
- * Process a synchronous request using coroutines
- */
-static int bdrv_rw_co(BdrvChild *child, int64_t sector_num, uint8_t *buf,
-                      int nb_sectors, bool is_write, BdrvRequestFlags flags)
-{
-    QEMUIOVector qiov;
-    struct iovec iov = {
-        .iov_base = (void *)buf,
-        .iov_len = nb_sectors * BDRV_SECTOR_SIZE,
-    };
-
-    if (nb_sectors < 0 || nb_sectors > BDRV_REQUEST_MAX_SECTORS) {
-        return -EINVAL;
-    }
-
-    qemu_iovec_init_external(&qiov, &iov, 1);
-    return bdrv_prwv_co(child, sector_num << BDRV_SECTOR_BITS,
-                        &qiov, is_write, flags);
-}
-
-/* return < 0 if error. See bdrv_write() for the return codes */
-int bdrv_read(BdrvChild *child, int64_t sector_num,
-              uint8_t *buf, int nb_sectors)
-{
-    return bdrv_rw_co(child, sector_num, buf, nb_sectors, false, 0);
-}
-
-/* Return < 0 if error. Important errors are:
-  -EIO         generic I/O error (may happen for all errors)
-  -ENOMEDIUM   No media inserted.
-  -EINVAL      Invalid sector number or nb_sectors
-  -EACCES      Trying to write a read-only device
-*/
-int bdrv_write(BdrvChild *child, int64_t sector_num,
-               const uint8_t *buf, int nb_sectors)
-{
-    return bdrv_rw_co(child, sector_num, (uint8_t *)buf, nb_sectors, true, 0);
-}

 int bdrv_pwrite_zeroes(BdrvChild *child, int64_t offset,
                        int bytes, BdrvRequestFlags flags)
@@ -776,7 +737,7 @@ int bdrv_pwrite_zeroes(BdrvChild *child, int64_t offset,
  * flags are passed through to bdrv_pwrite_zeroes (e.g. BDRV_REQ_MAY_UNMAP,
  * BDRV_REQ_FUA).
  *
- * Returns < 0 on error, 0 on success. For error codes see bdrv_write().
+ * Returns < 0 on error, 0 on success. For error codes see bdrv_pwrite().
  */
 int bdrv_make_zero(BdrvChild *child, BdrvRequestFlags flags)
 {
@@ -814,6 +775,7 @@ int bdrv_make_zero(BdrvChild *child, BdrvRequestFlags flags)
     }
 }

+/* return < 0 if error. See bdrv_pwrite() for the return codes */
 int bdrv_preadv(BdrvChild *child, int64_t offset, QEMUIOVector *qiov)
 {
     int ret;
@@ -854,6 +816,12 @@ int bdrv_pwritev(BdrvChild *child, int64_t offset, QEMUIOVector *qiov)
     return qiov->size;
 }

+/* Return < 0 if error. Important errors are:
+  -EIO         generic I/O error (may happen for all errors)
+  -ENOMEDIUM   No media inserted.
+  -EINVAL      Invalid sector number or nb_sectors
+  -EACCES      Trying to write a read-only device
+*/
 int bdrv_pwrite(BdrvChild *child, int64_t offset, const void *buf, int bytes)
 {
     QEMUIOVector qiov;
-- 
2.14.3

Re: [Qemu-devel] [Qemu-block] [PATCH 1/3] vdi: Switch to byte-based calls

[Alberto Garcia]

On Thu 26 Apr 2018 03:43:03 PM CEST, Eric Blake wrote:
> We are gradually moving away from sector-based interfaces, towards
> byte-based.  Make the change for the last few sector-based calls
> into the block layer from the vdi driver.
>
> Ideally, the vdi driver should switch to doing everything
> byte-based, but that's a more invasive change that requires a
> bit more auditing.
>
> Signed-off-by: Eric Blake <eblake@redhat.com>

Reviewed-by: Alberto Garcia <berto@igalia.com>

Berto

Re: [Qemu-devel] [Qemu-block] [PATCH 2/3] vvfat: Switch to byte-based calls

[Alberto Garcia]

On Thu 26 Apr 2018 03:43:04 PM CEST, Eric Blake wrote:
> We are gradually moving away from sector-based interfaces, towards
> byte-based.  Make the change for the last few sector-based calls
> into the block layer from the vvfat driver.
>
> Ideally, the vvfat driver should switch to doing everything
> byte-based, but that's a more invasive change that requires a
> bit more auditing.
>
> Signed-off-by: Eric Blake <eblake@redhat.com>

Reviewed-by: Alberto Garcia <berto@igalia.com>

Berto

Re: [Qemu-devel] [Qemu-block] [PATCH 3/3] block: Removed unused sector-based blocking I/O

[Alberto Garcia]

On Thu 26 Apr 2018 03:43:05 PM CEST, Eric Blake wrote:
> We are gradually moving away from sector-based interfaces, towards
> byte-based.  Now that all callers of blocking I/O have been converted
> to use our preferred byte-based bdrv_p{read,write}(), we can
> delete the unused bdrv_{read,write}().
>
> Signed-off-by: Eric Blake <eblake@redhat.com>

Reviewed-by: Alberto Garcia <berto@igalia.com>

> -static int bdrv_rw_co(BdrvChild *child, int64_t sector_num, uint8_t *buf,
> -                      int nb_sectors, bool is_write, BdrvRequestFlags flags)
> -{
> -    QEMUIOVector qiov;
> -    struct iovec iov = {
> -        .iov_base = (void *)buf,
> -        .iov_len = nb_sectors * BDRV_SECTOR_SIZE,
> -    };
> -
> -    if (nb_sectors < 0 || nb_sectors > BDRV_REQUEST_MAX_SECTORS) {
> -        return -EINVAL;
> -    }

Do we have a check for BDRV_REQUEST_MAX_BYTES in the byte-based API?

Berto

Re: [Qemu-devel] [Qemu-block] [PATCH 3/3] block: Removed unused sector-based blocking I/O

[Eric Blake]

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On 04/27/2018 09:01 AM, Alberto Garcia wrote:
> On Thu 26 Apr 2018 03:43:05 PM CEST, Eric Blake wrote:
>> We are gradually moving away from sector-based interfaces, towards
>> byte-based.  Now that all callers of blocking I/O have been converted
>> to use our preferred byte-based bdrv_p{read,write}(), we can
>> delete the unused bdrv_{read,write}().
>>
>> Signed-off-by: Eric Blake <eblake@redhat.com>
> 
> Reviewed-by: Alberto Garcia <berto@igalia.com>
> 
>> -static int bdrv_rw_co(BdrvChild *child, int64_t sector_num, uint8_t *buf,
>> -                      int nb_sectors, bool is_write, BdrvRequestFlags flags)
>> -{
>> -    QEMUIOVector qiov;
>> -    struct iovec iov = {
>> -        .iov_base = (void *)buf,
>> -        .iov_len = nb_sectors * BDRV_SECTOR_SIZE,
>> -    };
>> -
>> -    if (nb_sectors < 0 || nb_sectors > BDRV_REQUEST_MAX_SECTORS) {
>> -        return -EINVAL;
>> -    }
> 
> Do we have a check for BDRV_REQUEST_MAX_BYTES in the byte-based API?

No, but we don't need one.  First, note that bs->bl.max_transfer is
currently uint32_t, so right now, no driver can set it any larger than
4G; although they can certainly set it smaller (for example, NBD sets it
to 32M).  Then note that bdrv_co_pwritev() and friends take care of
fragmenting any >4G request down to max_transfer.  The old check was to
ensure that a sector count couldn't overflow larger than a 4G byte count
(since the sector API had a 32-bit intrinsic limit on byte count, even
though the parameter was in sectors); but the public byte-based API
doesn't have an intrinsic limit on byte count, and takes care of
fragmenting down to any intrinsic limit for the driver callbacks.

But, having said that, you've made me wonder if it's time to increase
max_transfer to [u]int64_t, then audit ALL drivers to ensure that they
either properly handle requests >=4G or else set max_transfer <4G
(ideally, the block layer will default max_transfer to the value of
BDRV_REQUEST_MAX_BYTES, even if the audit means we no longer need that
macro).  Should be a separate series, though.

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


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Re: [Qemu-devel] [Qemu-block] [PATCH 3/3] block: Removed unused sector-based blocking I/O

[Alberto Garcia]

On Fri 27 Apr 2018 05:43:33 PM CEST, Eric Blake wrote:
>>> -static int bdrv_rw_co(BdrvChild *child, int64_t sector_num, uint8_t *buf,
>>> -                      int nb_sectors, bool is_write, BdrvRequestFlags flags)
>>> -{
>>> -    QEMUIOVector qiov;
>>> -    struct iovec iov = {
>>> -        .iov_base = (void *)buf,
>>> -        .iov_len = nb_sectors * BDRV_SECTOR_SIZE,
>>> -    };
>>> -
>>> -    if (nb_sectors < 0 || nb_sectors > BDRV_REQUEST_MAX_SECTORS) {
>>> -        return -EINVAL;
>>> -    }
>> 
>> Do we have a check for BDRV_REQUEST_MAX_BYTES in the byte-based API?
>
> No, but we don't need one.  First, note that bs->bl.max_transfer is
> currently uint32_t, so right now, no driver can set it any larger than
> 4G

But note that the old limit was based on a signed integer.

BDRV_REQUEST_MAX_SECTORS is 2147483136 bytes (a bit less than 2GB).

For 32-bit integers, (INT_MAX - 1) & ~511 = 2147483136

Berto

Re: [Qemu-devel] [Qemu-block] [PATCH 3/3] block: Removed unused sector-based blocking I/O

[Stefan Hajnoczi]

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On Thu, Apr 26, 2018 at 08:43:05AM -0500, Eric Blake wrote:
> We are gradually moving away from sector-based interfaces, towards
> byte-based.  Now that all callers of blocking I/O have been converted
> to use our preferred byte-based bdrv_p{read,write}(), we can
> delete the unused bdrv_{read,write}().
> 
> Signed-off-by: Eric Blake <eblake@redhat.com>
> ---
>  include/block/block.h |  4 ----
>  block/io.c            | 48 ++++++++----------------------------------------
>  2 files changed, 8 insertions(+), 44 deletions(-)

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>

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Re: [Qemu-devel] [Qemu-block] [PATCH 3/3] block: Removed unused sector-based blocking I/O

[Eric Blake]

[Reviving an old series]

On 5/3/18 8:36 AM, Alberto Garcia wrote:
> On Fri 27 Apr 2018 05:43:33 PM CEST, Eric Blake wrote:
>>>> -static int bdrv_rw_co(BdrvChild *child, int64_t sector_num, uint8_t *buf,
>>>> -                      int nb_sectors, bool is_write, BdrvRequestFlags flags)
>>>> -{
>>>> -    QEMUIOVector qiov;
>>>> -    struct iovec iov = {
>>>> -        .iov_base = (void *)buf,
>>>> -        .iov_len = nb_sectors * BDRV_SECTOR_SIZE,
>>>> -    };
>>>> -
>>>> -    if (nb_sectors < 0 || nb_sectors > BDRV_REQUEST_MAX_SECTORS) {
>>>> -        return -EINVAL;
>>>> -    }
>>>
>>> Do we have a check for BDRV_REQUEST_MAX_BYTES in the byte-based API?
>>
>> No, but we don't need one.  First, note that bs->bl.max_transfer is
>> currently uint32_t, so right now, no driver can set it any larger than
>> 4G
> 
> But note that the old limit was based on a signed integer.
> 
> BDRV_REQUEST_MAX_SECTORS is 2147483136 bytes (a bit less than 2GB).
> 
> For 32-bit integers, (INT_MAX - 1) & ~511 = 2147483136

The whole point of the byte-based callbacks is that they pass a 64-bit 
length BUT also honor the driver's max_transfer.  As long as drivers 
default to (or explicitly set) a max_transfer of 
BDRV_REQUEST_MAX_SECTORS or smaller, then the block layer has already 
taken care of fragmenting things so that the callers no longer have to 
worry about artificially fragmenting things themselves before handing 
something to the block layer that might overflow.  And you snipped the 
rest of my mail, where I argued:

> 
> But, having said that, you've made me wonder if it's time to increase
> max_transfer to [u]int64_t, then audit ALL drivers to ensure that they
> either properly handle requests >=4G or else set max_transfer <4G
> (ideally, the block layer will default max_transfer to the value of
> BDRV_REQUEST_MAX_BYTES, even if the audit means we no longer need that
> macro).  Should be a separate series, though.

I will concede that you are right that because we previously used a 
signed type, I should amend my argument to state that we should audit 
ALL drivers to ensure that they either properly handle requests >= 2G 
or else set max_transfer <2G, even though max_transfer is unsigned. 
Maybe it's time that I attempt that audit, before posting a v2 of this 
series for 4.0. (Fingers crossed that it will be a quick audit)

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