[pve-devel] [PATCH qemu] fix #7033: backport fixes for write zeroes request alignment to fix qcow2 creation on LVM

* [pve-devel] [PATCH qemu] fix #7033: backport fixes for write zeroes request alignment to fix qcow2 creation on LVM
@ 2025-11-19 15:11 Fiona Ebner
  2025-11-19 17:13 ` Thomas Lamprecht
  0 siblings, 1 reply; 2+ messages in thread
From: Fiona Ebner @ 2025-11-19 15:11 UTC (permalink / raw)
  To: pve-devel

As also outlined in [0], QEMU 10.1 introduced a regression here, with
a fix [1] already on qemu-devel. The issue was also reported in the
community forum [2], thanks to Abobakr for pointing me towards the
upstream issue!

[0]: https://gitlab.com/qemu-project/qemu/-/issues/3127
[1]: https://lore.kernel.org/qemu-devel/20251007141700.71891-1-stefanha@redhat.com/
[2]: https://forum.proxmox.com/threads/vm-create-move-fails-on-netapp-shared-lvm-storage-with-qcow2-disk.175785/

Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
---
 ...six-populate-pwrite_zeroes_alignment.patch | 49 +++++++++++
 ..._zeroes_alignment-when-writing-first.patch | 86 +++++++++++++++++++
 ...k-file-change-locking-default-to-off.patch |  2 +-
 ...le-posix-make-locking-optiono-on-cre.patch | 14 +--
 debian/patches/series                         |  2 +
 5 files changed, 145 insertions(+), 8 deletions(-)
 create mode 100644 debian/patches/extra/0009-file-posix-populate-pwrite_zeroes_alignment.patch
 create mode 100644 debian/patches/extra/0010-block-use-pwrite_zeroes_alignment-when-writing-first.patch

diff --git a/debian/patches/extra/0009-file-posix-populate-pwrite_zeroes_alignment.patch b/debian/patches/extra/0009-file-posix-populate-pwrite_zeroes_alignment.patch
new file mode 100644
index 0000000..513a8c7
--- /dev/null
+++ b/debian/patches/extra/0009-file-posix-populate-pwrite_zeroes_alignment.patch
@@ -0,0 +1,49 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Stefan Hajnoczi <stefanha@redhat.com>
+Date: Tue, 7 Oct 2025 10:16:58 -0400
+Subject: [PATCH] file-posix: populate pwrite_zeroes_alignment
+
+Linux block devices require write zeroes alignment whereas files do not.
+
+It may come as a surprise that block devices opened in buffered I/O mode
+require the alignment for write zeroes requests although normal
+read/write requests do not.
+
+Therefore it is necessary to populate the pwrite_zeroes_alignment field.
+
+Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
+Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
+Link: https://lore.proxmox.com/20251007141700.71891-2-stefanha@redhat.com
+[FE: picked from qemu-devel]
+Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
+---
+ block/file-posix.c | 16 ++++++++++++++++
+ 1 file changed, 16 insertions(+)
+
+diff --git a/block/file-posix.c b/block/file-posix.c
+index 8c738674ce..827ffa77a5 100644
+--- a/block/file-posix.c
++++ b/block/file-posix.c
+@@ -1602,6 +1602,22 @@ static void raw_refresh_limits(BlockDriverState *bs, Error **errp)
+ 
+             bs->bl.pdiscard_alignment = dalign;
+         }
++
++#ifdef __linux__
++        /*
++         * Linux requires logical block size alignment for write zeroes even
++         * when normal reads/writes do not require alignment.
++         */
++        if (!s->needs_alignment) {
++            ret = probe_logical_blocksize(s->fd,
++                                          &bs->bl.pwrite_zeroes_alignment);
++            if (ret < 0) {
++                error_setg_errno(errp, -ret,
++                                 "Failed to probe logical block size");
++                return;
++            }
++        }
++#endif /* __linux__ */
+     }
+ 
+     raw_refresh_zoned_limits(bs, &st, errp);
diff --git a/debian/patches/extra/0010-block-use-pwrite_zeroes_alignment-when-writing-first.patch b/debian/patches/extra/0010-block-use-pwrite_zeroes_alignment-when-writing-first.patch
new file mode 100644
index 0000000..de057ae
--- /dev/null
+++ b/debian/patches/extra/0010-block-use-pwrite_zeroes_alignment-when-writing-first.patch
@@ -0,0 +1,86 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Stefan Hajnoczi <stefanha@redhat.com>
+Date: Tue, 7 Oct 2025 10:16:59 -0400
+Subject: [PATCH] block: use pwrite_zeroes_alignment when writing first sector
+
+Since commit 5634622bcb33 ("file-posix: allow BLKZEROOUT with -t
+writeback"), qemu-img create errors out on a Linux loop block device
+with a 4 KB sector size:
+
+  # dd if=/dev/zero of=blockfile bs=1M count=1024
+  # losetup --sector-size 4096 /dev/loop0 blockfile
+  # qemu-img create -f raw /dev/loop0 1G
+  Formatting '/dev/loop0', fmt=raw size=1073741824
+  qemu-img: /dev/loop0: Failed to clear the new image's first sector: Invalid argument
+
+Use the pwrite_zeroes_alignment block limit to avoid misaligned
+fallocate(2) or ioctl(BLKZEROOUT) in the block/file-posix.c block
+driver.
+
+Fixes: 5634622bcb33 ("file-posix: allow BLKZEROOUT with -t writeback")
+Reported-by: Jean-Louis Dupond <jean-louis@dupond.be>
+Buglink: https://gitlab.com/qemu-project/qemu/-/issues/3127
+Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
+Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
+Link: https://lore.proxmox.com/20251007141700.71891-3-stefanha@redhat.com
+[FE: picked from qemu-devel]
+Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
+---
+ block.c                           |  3 ++-
+ block/block-backend.c             | 11 +++++++++++
+ include/system/block-backend-io.h |  1 +
+ 3 files changed, 14 insertions(+), 1 deletion(-)
+
+diff --git a/block.c b/block.c
+index 8848e9a7ed..be77e03904 100644
+--- a/block.c
++++ b/block.c
+@@ -606,12 +606,13 @@ create_file_fallback_zero_first_sector(BlockBackend *blk,
+                                        int64_t current_size,
+                                        Error **errp)
+ {
++    uint32_t alignment = blk_get_pwrite_zeroes_alignment(blk);
+     int64_t bytes_to_clear;
+     int ret;
+ 
+     GLOBAL_STATE_CODE();
+ 
+-    bytes_to_clear = MIN(current_size, BDRV_SECTOR_SIZE);
++    bytes_to_clear = MIN(current_size, MAX(BDRV_SECTOR_SIZE, alignment));
+     if (bytes_to_clear) {
+         ret = blk_co_pwrite_zeroes(blk, 0, bytes_to_clear, BDRV_REQ_MAY_UNMAP);
+         if (ret < 0) {
+diff --git a/block/block-backend.c b/block/block-backend.c
+index f8d6ba65c1..239d6eca37 100644
+--- a/block/block-backend.c
++++ b/block/block-backend.c
+@@ -2305,6 +2305,17 @@ uint32_t blk_get_request_alignment(BlockBackend *blk)
+     return bs ? bs->bl.request_alignment : BDRV_SECTOR_SIZE;
+ }
+ 
++/* Returns the optimal write zeroes alignment, in bytes; guaranteed nonzero */
++uint32_t blk_get_pwrite_zeroes_alignment(BlockBackend *blk)
++{
++    BlockDriverState *bs = blk_bs(blk);
++    IO_CODE();
++    if (!bs) {
++        return BDRV_SECTOR_SIZE;
++    }
++    return bs->bl.pwrite_zeroes_alignment ?: bs->bl.request_alignment;
++}
++
+ /* Returns the maximum hardware transfer length, in bytes; guaranteed nonzero */
+ uint64_t blk_get_max_hw_transfer(BlockBackend *blk)
+ {
+diff --git a/include/system/block-backend-io.h b/include/system/block-backend-io.h
+index ba8dfcc7d0..6d5ac476fc 100644
+--- a/include/system/block-backend-io.h
++++ b/include/system/block-backend-io.h
+@@ -116,6 +116,7 @@ BlockAIOCB *blk_abort_aio_request(BlockBackend *blk,
+                                   void *opaque, int ret);
+ 
+ uint32_t blk_get_request_alignment(BlockBackend *blk);
++uint32_t blk_get_pwrite_zeroes_alignment(BlockBackend *blk);
+ uint32_t blk_get_max_transfer(BlockBackend *blk);
+ uint64_t blk_get_max_hw_transfer(BlockBackend *blk);
+ 
diff --git a/debian/patches/pve/0001-PVE-Config-block-file-change-locking-default-to-off.patch b/debian/patches/pve/0001-PVE-Config-block-file-change-locking-default-to-off.patch
index 2538947..df81614 100644
--- a/debian/patches/pve/0001-PVE-Config-block-file-change-locking-default-to-off.patch
+++ b/debian/patches/pve/0001-PVE-Config-block-file-change-locking-default-to-off.patch
@@ -14,7 +14,7 @@ Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
  1 file changed, 2 insertions(+), 2 deletions(-)
 
 diff --git a/block/file-posix.c b/block/file-posix.c
-index 8c738674ce..6a9433c836 100644
+index 827ffa77a5..baac7653db 100644
 --- a/block/file-posix.c
 +++ b/block/file-posix.c
 @@ -588,7 +588,7 @@ static QemuOptsList raw_runtime_opts = {
diff --git a/debian/patches/pve/0022-PVE-Up-Config-file-posix-make-locking-optiono-on-cre.patch b/debian/patches/pve/0022-PVE-Up-Config-file-posix-make-locking-optiono-on-cre.patch
index 270829f..989695e 100644
--- a/debian/patches/pve/0022-PVE-Up-Config-file-posix-make-locking-optiono-on-cre.patch
+++ b/debian/patches/pve/0022-PVE-Up-Config-file-posix-make-locking-optiono-on-cre.patch
@@ -13,10 +13,10 @@ Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
  2 files changed, 46 insertions(+), 20 deletions(-)
 
 diff --git a/block/file-posix.c b/block/file-posix.c
-index 6a9433c836..37b6d495db 100644
+index baac7653db..fc5cf223bc 100644
 --- a/block/file-posix.c
 +++ b/block/file-posix.c
-@@ -2977,6 +2977,7 @@ raw_co_create(BlockdevCreateOptions *options, Error **errp)
+@@ -2993,6 +2993,7 @@ raw_co_create(BlockdevCreateOptions *options, Error **errp)
      int fd;
      uint64_t perm, shared;
      int result = 0;
@@ -24,7 +24,7 @@ index 6a9433c836..37b6d495db 100644
  
      /* Validate options and set default values */
      assert(options->driver == BLOCKDEV_DRIVER_FILE);
-@@ -3017,19 +3018,22 @@ raw_co_create(BlockdevCreateOptions *options, Error **errp)
+@@ -3033,19 +3034,22 @@ raw_co_create(BlockdevCreateOptions *options, Error **errp)
      perm = BLK_PERM_WRITE | BLK_PERM_RESIZE;
      shared = BLK_PERM_ALL & ~BLK_PERM_RESIZE;
  
@@ -59,7 +59,7 @@ index 6a9433c836..37b6d495db 100644
      }
  
      /* Clear the file by truncating it to 0 */
-@@ -3083,13 +3087,15 @@ raw_co_create(BlockdevCreateOptions *options, Error **errp)
+@@ -3099,13 +3103,15 @@ raw_co_create(BlockdevCreateOptions *options, Error **errp)
      }
  
  out_unlock:
@@ -82,7 +82,7 @@ index 6a9433c836..37b6d495db 100644
      }
  
  out_close:
-@@ -3113,6 +3119,7 @@ raw_co_create_opts(BlockDriver *drv, const char *filename,
+@@ -3129,6 +3135,7 @@ raw_co_create_opts(BlockDriver *drv, const char *filename,
      PreallocMode prealloc;
      char *buf = NULL;
      Error *local_err = NULL;
@@ -90,7 +90,7 @@ index 6a9433c836..37b6d495db 100644
  
      /* Skip file: protocol prefix */
      strstart(filename, "file:", &filename);
-@@ -3135,6 +3142,18 @@ raw_co_create_opts(BlockDriver *drv, const char *filename,
+@@ -3151,6 +3158,18 @@ raw_co_create_opts(BlockDriver *drv, const char *filename,
          return -EINVAL;
      }
  
@@ -109,7 +109,7 @@ index 6a9433c836..37b6d495db 100644
      options = (BlockdevCreateOptions) {
          .driver     = BLOCKDEV_DRIVER_FILE,
          .u.file     = {
-@@ -3146,6 +3165,8 @@ raw_co_create_opts(BlockDriver *drv, const char *filename,
+@@ -3162,6 +3181,8 @@ raw_co_create_opts(BlockDriver *drv, const char *filename,
              .nocow              = nocow,
              .has_extent_size_hint = has_extent_size_hint,
              .extent_size_hint   = extent_size_hint,
diff --git a/debian/patches/series b/debian/patches/series
index 0bd9ea8..b1afcd4 100644
--- a/debian/patches/series
+++ b/debian/patches/series
@@ -6,6 +6,8 @@ extra/0005-hw-scsi-avoid-deadlock-upon-TMF-request-cancelling-w.patch
 extra/0006-vfio-rename-field-to-num_initial_regions.patch
 extra/0007-vfio-only-check-region-info-cache-for-initial-region.patch
 extra/0008-ui-vdagent-fix-windows-agent-regression.patch
+extra/0009-file-posix-populate-pwrite_zeroes_alignment.patch
+extra/0010-block-use-pwrite_zeroes_alignment-when-writing-first.patch
 bitmap-mirror/0001-drive-mirror-add-support-for-sync-bitmap-mode-never.patch
 bitmap-mirror/0002-drive-mirror-add-support-for-conditional-and-always-.patch
 bitmap-mirror/0003-mirror-add-check-for-bitmap-mode-without-bitmap.patch
-- 
2.47.3



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