[PATCH v3 0/4] block: fix detect-zeroes= with BDRV_REQ_REGISTERED_BUF

[PATCH v3 0/4] block: fix detect-zeroes= with BDRV_REQ_REGISTERED_BUF

[Stefan Hajnoczi]

v3:
- Restore alphabetical order in getopt strings [Eric]
v2:
- Add comment explaining unbalanced error code path in
  qemu_io_alloc_from_file() [Eric]
- List options alphabetically in help output [Eric]
- Add Tested-by/Reviewed-by
- CC qemu-stable on the fix

The first patch fixes a regression in QEMU 7.2 where detect-zeroes breaks with
virtio-blk devices due to a BDRV_REQ_REGISTERED_BUF bug. Details of the
regression can be found here:
https://gitlab.com/qemu-project/qemu/-/issues/1404

The remaining patches add a regression test that will protect this code path in
the future. The qemu-io command is extended with the new -r option that calls
blk_register_buf(). This allows a qemu-iotests test case to trigger the same
bug as virtio-blk.

Stefan Hajnoczi (4):
  block: fix detect-zeroes= with BDRV_REQ_REGISTERED_BUF
  qemu-io: use BdrvRequestFlags instead of int
  qemu-io: add -r option to register I/O buffer
  iotests/detect-zeroes-registered-buf: add new test

 block/io.c                                    |   3 +
 qemu-io-cmds.c                                | 180 ++++++++++++------
 .../tests/detect-zeroes-registered-buf        |  58 ++++++
 .../tests/detect-zeroes-registered-buf.out    |   7 +
 4 files changed, 189 insertions(+), 59 deletions(-)
 create mode 100755 tests/qemu-iotests/tests/detect-zeroes-registered-buf
 create mode 100644 tests/qemu-iotests/tests/detect-zeroes-registered-buf.out

-- 
2.39.1

[PATCH v3 1/4] block: fix detect-zeroes= with BDRV_REQ_REGISTERED_BUF

[Stefan Hajnoczi]

When a write request is converted into a write zeroes request by the
detect-zeroes= feature, it is no longer associated with an I/O buffer.
The BDRV_REQ_REGISTERED_BUF flag doesn't make sense without an I/O
buffer and must be cleared because bdrv_co_do_pwrite_zeroes() fails with
-EINVAL when it's set.

Fiona Ebner <f.ebner@proxmox.com> bisected and diagnosed this QEMU 7.2
regression where writes containing zeroes to a blockdev with
discard=unmap,detect-zeroes=unmap fail.

Buglink: https://gitlab.com/qemu-project/qemu/-/issues/1404
Fixes: e8b6535533be ("block: add BDRV_REQ_REGISTERED_BUF request flag")
Tested-by: Fiona Ebner <f.ebner@proxmox.com>
Cc: qemu-stable@nongnu.org
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 block/io.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/block/io.c b/block/io.c
index a09a19f7a7..24a2bc42d3 100644
--- a/block/io.c
+++ b/block/io.c
@@ -1926,6 +1926,9 @@ static int coroutine_fn bdrv_aligned_pwritev(BdrvChild *child,
         if (bs->detect_zeroes == BLOCKDEV_DETECT_ZEROES_OPTIONS_UNMAP) {
             flags |= BDRV_REQ_MAY_UNMAP;
         }
+
+        /* Can't use optimization hint with bufferless zero write */
+        flags &= ~BDRV_REQ_REGISTERED_BUF;
     }
 
     if (ret < 0) {
-- 
2.39.1

Re: [PATCH v3 1/4] block: fix detect-zeroes= with BDRV_REQ_REGISTERED_BUF

[Hanna Czenczek]

On 01.02.23 16:27, Stefan Hajnoczi wrote:
> When a write request is converted into a write zeroes request by the
> detect-zeroes= feature, it is no longer associated with an I/O buffer.
> The BDRV_REQ_REGISTERED_BUF flag doesn't make sense without an I/O
> buffer and must be cleared because bdrv_co_do_pwrite_zeroes() fails with
> -EINVAL when it's set.
>
> Fiona Ebner <f.ebner@proxmox.com> bisected and diagnosed this QEMU 7.2
> regression where writes containing zeroes to a blockdev with
> discard=unmap,detect-zeroes=unmap fail.
>
> Buglink: https://gitlab.com/qemu-project/qemu/-/issues/1404
> Fixes: e8b6535533be ("block: add BDRV_REQ_REGISTERED_BUF request flag")
> Tested-by: Fiona Ebner <f.ebner@proxmox.com>
> Cc: qemu-stable@nongnu.org
> Reviewed-by: Eric Blake <eblake@redhat.com>
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
>   block/io.c | 3 +++
>   1 file changed, 3 insertions(+)

Reviewed-by: Hanna Czenczek <hreitz@redhat.com>

[PATCH v3 2/4] qemu-io: use BdrvRequestFlags instead of int

[Stefan Hajnoczi]

The block layer APIs use BdrvRequestFlags while qemu-io code uses int.
Although the code compiles and runs fine, BdrvRequestFlags is clearer
because it differentiates between other types of flags like bdrv_open()
flags.

This is purely refactoring.

Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 qemu-io-cmds.c | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/qemu-io-cmds.c b/qemu-io-cmds.c
index 952dc940f1..c0125d14c0 100644
--- a/qemu-io-cmds.c
+++ b/qemu-io-cmds.c
@@ -556,7 +556,7 @@ static int do_pread(BlockBackend *blk, char *buf, int64_t offset,
 }
 
 static int do_pwrite(BlockBackend *blk, char *buf, int64_t offset,
-                     int64_t bytes, int flags, int64_t *total)
+                     int64_t bytes, BdrvRequestFlags flags, int64_t *total)
 {
     int ret;
 
@@ -577,7 +577,7 @@ typedef struct {
     int64_t offset;
     int64_t bytes;
     int64_t *total;
-    int flags;
+    BdrvRequestFlags flags;
     int ret;
     bool done;
 } CoWriteZeroes;
@@ -598,7 +598,8 @@ static void coroutine_fn co_pwrite_zeroes_entry(void *opaque)
 }
 
 static int do_co_pwrite_zeroes(BlockBackend *blk, int64_t offset,
-                               int64_t bytes, int flags, int64_t *total)
+                               int64_t bytes, BdrvRequestFlags flags,
+                               int64_t *total)
 {
     Coroutine *co;
     CoWriteZeroes data = {
@@ -688,7 +689,7 @@ static int do_aio_readv(BlockBackend *blk, QEMUIOVector *qiov,
 }
 
 static int do_aio_writev(BlockBackend *blk, QEMUIOVector *qiov,
-                         int64_t offset, int flags, int *total)
+                         int64_t offset, BdrvRequestFlags flags, int *total)
 {
     int async_ret = NOT_DONE;
 
@@ -1065,7 +1066,7 @@ static int write_f(BlockBackend *blk, int argc, char **argv)
     struct timespec t1, t2;
     bool Cflag = false, qflag = false, bflag = false;
     bool Pflag = false, zflag = false, cflag = false, sflag = false;
-    int flags = 0;
+    BdrvRequestFlags flags = 0;
     int c, cnt, ret;
     char *buf = NULL;
     int64_t offset;
@@ -1266,7 +1267,7 @@ static int writev_f(BlockBackend *blk, int argc, char **argv)
 {
     struct timespec t1, t2;
     bool Cflag = false, qflag = false;
-    int flags = 0;
+    BdrvRequestFlags flags = 0;
     int c, cnt, ret;
     char *buf;
     int64_t offset;
@@ -1581,7 +1582,7 @@ static int aio_write_f(BlockBackend *blk, int argc, char **argv)
     int nr_iov, c;
     int pattern = 0xcd;
     struct aio_ctx *ctx = g_new0(struct aio_ctx, 1);
-    int flags = 0;
+    BdrvRequestFlags flags = 0;
 
     ctx->blk = blk;
     while ((c = getopt(argc, argv, "CfiqP:uz")) != -1) {
-- 
2.39.1

Re: [PATCH v3 2/4] qemu-io: use BdrvRequestFlags instead of int

[Hanna Czenczek]

On 01.02.23 16:27, Stefan Hajnoczi wrote:
> The block layer APIs use BdrvRequestFlags while qemu-io code uses int.
> Although the code compiles and runs fine, BdrvRequestFlags is clearer
> because it differentiates between other types of flags like bdrv_open()
> flags.
>
> This is purely refactoring.
>
> Reviewed-by: Eric Blake <eblake@redhat.com>
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
>   qemu-io-cmds.c | 15 ++++++++-------
>   1 file changed, 8 insertions(+), 7 deletions(-)

With a rebase on264dcbb2b1e5b66d7a5b08662b200c2b315dce0f:

Reviewed-by: Hanna Czenczek <hreitz@redhat.com>

[PATCH v3 3/4] qemu-io: add -r option to register I/O buffer

[Stefan Hajnoczi]

The blk_register_buf() API is an optimization hint that allows some
block drivers to avoid I/O buffer housekeeping or bounce buffers.

Add an -r option to register the I/O buffer so that qemu-io can be used
to test the blk_register_buf() API. The next commit will add a test that
uses the new option.

Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 qemu-io-cmds.c | 167 +++++++++++++++++++++++++++++++++----------------
 1 file changed, 114 insertions(+), 53 deletions(-)

diff --git a/qemu-io-cmds.c b/qemu-io-cmds.c
index c0125d14c0..4b8dbef36d 100644
--- a/qemu-io-cmds.c
+++ b/qemu-io-cmds.c
@@ -338,7 +338,8 @@ static int parse_pattern(const char *arg)
  */
 
 #define MISALIGN_OFFSET     16
-static void *qemu_io_alloc(BlockBackend *blk, size_t len, int pattern)
+static void *qemu_io_alloc(BlockBackend *blk, size_t len, int pattern,
+                           bool register_buf)
 {
     void *buf;
 
@@ -347,17 +348,24 @@ static void *qemu_io_alloc(BlockBackend *blk, size_t len, int pattern)
     }
     buf = blk_blockalign(blk, len);
     memset(buf, pattern, len);
+    if (register_buf) {
+        blk_register_buf(blk, buf, len, &error_abort);
+    }
     if (qemuio_misalign) {
         buf += MISALIGN_OFFSET;
     }
     return buf;
 }
 
-static void qemu_io_free(void *p)
+static void qemu_io_free(BlockBackend *blk, void *p, size_t len,
+                         bool unregister_buf)
 {
     if (qemuio_misalign) {
         p -= MISALIGN_OFFSET;
     }
+    if (unregister_buf) {
+        blk_unregister_buf(blk, p, len);
+    }
     qemu_vfree(p);
 }
 
@@ -371,12 +379,13 @@ static void qemu_io_free(void *p)
  * @blk - the block backend where the buffer content is going to be written to
  * @len - the buffer length
  * @file_name - the file to read the content from
+ * @register_buf - call blk_register_buf()
  *
  * Returns: the buffer pointer on success
  *          NULL on error
  */
 static void *qemu_io_alloc_from_file(BlockBackend *blk, size_t len,
-                                     const char *file_name)
+                                     const char *file_name, bool register_buf)
 {
     char *buf, *buf_origin;
     FILE *f = fopen(file_name, "r");
@@ -414,6 +423,10 @@ static void *qemu_io_alloc_from_file(BlockBackend *blk, size_t len,
     fclose(f);
     f = NULL;
 
+    if (register_buf) {
+        blk_register_buf(blk, buf_origin, len, &error_abort);
+    }
+
     if (len > pattern_len) {
         len -= pattern_len;
         buf += pattern_len;
@@ -431,7 +444,11 @@ static void *qemu_io_alloc_from_file(BlockBackend *blk, size_t len,
     return buf_origin;
 
 error:
-    qemu_io_free(buf_origin);
+    /*
+     * This code path is only taken before blk_register_buf() is called, so
+     * hardcode the qemu_io_free() unregister_buf argument to false.
+     */
+    qemu_io_free(blk, buf_origin, len, false);
     if (f) {
         fclose(f);
     }
@@ -490,7 +507,7 @@ static void print_report(const char *op, struct timespec *t, int64_t offset,
  */
 static void *
 create_iovec(BlockBackend *blk, QEMUIOVector *qiov, char **argv, int nr_iov,
-             int pattern)
+             int pattern, bool register_buf)
 {
     size_t *sizes = g_new0(size_t, nr_iov);
     size_t count = 0;
@@ -526,7 +543,7 @@ create_iovec(BlockBackend *blk, QEMUIOVector *qiov, char **argv, int nr_iov,
 
     qemu_iovec_init(qiov, nr_iov);
 
-    buf = p = qemu_io_alloc(blk, count, pattern);
+    buf = p = qemu_io_alloc(blk, count, pattern, register_buf);
 
     for (i = 0; i < nr_iov; i++) {
         qemu_iovec_add(qiov, p, sizes[i]);
@@ -539,7 +556,7 @@ fail:
 }
 
 static int do_pread(BlockBackend *blk, char *buf, int64_t offset,
-                    int64_t bytes, int64_t *total)
+                    int64_t bytes, BdrvRequestFlags flags, int64_t *total)
 {
     int ret;
 
@@ -547,7 +564,7 @@ static int do_pread(BlockBackend *blk, char *buf, int64_t offset,
         return -ERANGE;
     }
 
-    ret = blk_pread(blk, offset, bytes, (uint8_t *)buf, 0);
+    ret = blk_pread(blk, offset, bytes, (uint8_t *)buf, flags);
     if (ret < 0) {
         return ret;
     }
@@ -675,11 +692,11 @@ static void aio_rw_done(void *opaque, int ret)
 }
 
 static int do_aio_readv(BlockBackend *blk, QEMUIOVector *qiov,
-                        int64_t offset, int *total)
+                        int64_t offset, BdrvRequestFlags flags, int *total)
 {
     int async_ret = NOT_DONE;
 
-    blk_aio_preadv(blk, offset, qiov, 0, aio_rw_done, &async_ret);
+    blk_aio_preadv(blk, offset, qiov, flags, aio_rw_done, &async_ret);
     while (async_ret == NOT_DONE) {
         main_loop_wait(false);
     }
@@ -719,6 +736,7 @@ static void read_help(void)
 " -p, -- ignored for backwards compatibility\n"
 " -P, -- use a pattern to verify read data\n"
 " -q, -- quiet mode, do not show I/O statistics\n"
+" -r, -- register I/O buffer\n"
 " -s, -- start offset for pattern verification (only with -P)\n"
 " -v, -- dump buffer to standard output\n"
 "\n");
@@ -732,7 +750,7 @@ static const cmdinfo_t read_cmd = {
     .cfunc      = read_f,
     .argmin     = 2,
     .argmax     = -1,
-    .args       = "[-abCqv] [-P pattern [-s off] [-l len]] off len",
+    .args       = "[-abCqrv] [-P pattern [-s off] [-l len]] off len",
     .oneline    = "reads a number of bytes at a specified offset",
     .help       = read_help,
 };
@@ -750,6 +768,7 @@ static int read_f(BlockBackend *blk, int argc, char **argv)
     int64_t total = 0;
     int pattern = 0;
     int64_t pattern_offset = 0, pattern_count = 0;
+    BdrvRequestFlags flags = 0;
 
     while ((c = getopt(argc, argv, "bCl:pP:qs:v")) != -1) {
         switch (c) {
@@ -780,6 +799,9 @@ static int read_f(BlockBackend *blk, int argc, char **argv)
         case 'q':
             qflag = true;
             break;
+        case 'r':
+            flags |= BDRV_REQ_REGISTERED_BUF;
+            break;
         case 's':
             sflag = true;
             pattern_offset = cvtnum(optarg);
@@ -844,15 +866,20 @@ static int read_f(BlockBackend *blk, int argc, char **argv)
                    count);
             return -EINVAL;
         }
+        if (flags & BDRV_REQ_REGISTERED_BUF) {
+            printf("I/O buffer registration is not supported when reading "
+                    "from vmstate\n");
+            return -EINVAL;
+        }
     }
 
-    buf = qemu_io_alloc(blk, count, 0xab);
+    buf = qemu_io_alloc(blk, count, 0xab, flags & BDRV_REQ_REGISTERED_BUF);
 
     clock_gettime(CLOCK_MONOTONIC, &t1);
     if (bflag) {
         ret = do_load_vmstate(blk, buf, offset, count, &total);
     } else {
-        ret = do_pread(blk, buf, offset, count, &total);
+        ret = do_pread(blk, buf, offset, count, flags, &total);
     }
     clock_gettime(CLOCK_MONOTONIC, &t2);
 
@@ -889,7 +916,7 @@ static int read_f(BlockBackend *blk, int argc, char **argv)
     print_report("read", &t2, offset, count, total, cnt, Cflag);
 
 out:
-    qemu_io_free(buf);
+    qemu_io_free(blk, buf, count, flags & BDRV_REQ_REGISTERED_BUF);
     return ret;
 }
 
@@ -907,8 +934,9 @@ static void readv_help(void)
 " Uses multiple iovec buffers if more than one byte range is specified.\n"
 " -C, -- report statistics in a machine parsable format\n"
 " -P, -- use a pattern to verify read data\n"
-" -v, -- dump buffer to standard output\n"
 " -q, -- quiet mode, do not show I/O statistics\n"
+" -r, -- register I/O buffer\n"
+" -v, -- dump buffer to standard output\n"
 "\n");
 }
 
@@ -919,7 +947,7 @@ static const cmdinfo_t readv_cmd = {
     .cfunc      = readv_f,
     .argmin     = 2,
     .argmax     = -1,
-    .args       = "[-Cqv] [-P pattern] off len [len..]",
+    .args       = "[-Cqrv] [-P pattern] off len [len..]",
     .oneline    = "reads a number of bytes at a specified offset",
     .help       = readv_help,
 };
@@ -937,8 +965,9 @@ static int readv_f(BlockBackend *blk, int argc, char **argv)
     QEMUIOVector qiov;
     int pattern = 0;
     bool Pflag = false;
+    BdrvRequestFlags flags = 0;
 
-    while ((c = getopt(argc, argv, "CP:qv")) != -1) {
+    while ((c = getopt(argc, argv, "CP:qrv")) != -1) {
         switch (c) {
         case 'C':
             Cflag = true;
@@ -953,6 +982,9 @@ static int readv_f(BlockBackend *blk, int argc, char **argv)
         case 'q':
             qflag = true;
             break;
+        case 'r':
+            flags |= BDRV_REQ_REGISTERED_BUF;
+            break;
         case 'v':
             vflag = true;
             break;
@@ -976,13 +1008,14 @@ static int readv_f(BlockBackend *blk, int argc, char **argv)
     optind++;
 
     nr_iov = argc - optind;
-    buf = create_iovec(blk, &qiov, &argv[optind], nr_iov, 0xab);
+    buf = create_iovec(blk, &qiov, &argv[optind], nr_iov, 0xab,
+                       flags & BDRV_REQ_REGISTERED_BUF);
     if (buf == NULL) {
         return -EINVAL;
     }
 
     clock_gettime(CLOCK_MONOTONIC, &t1);
-    ret = do_aio_readv(blk, &qiov, offset, &total);
+    ret = do_aio_readv(blk, &qiov, offset, flags, &total);
     clock_gettime(CLOCK_MONOTONIC, &t2);
 
     if (ret < 0) {
@@ -1017,8 +1050,8 @@ static int readv_f(BlockBackend *blk, int argc, char **argv)
     print_report("read", &t2, offset, qiov.size, total, cnt, Cflag);
 
 out:
+    qemu_io_free(blk, buf, qiov.size, flags & BDRV_REQ_REGISTERED_BUF);
     qemu_iovec_destroy(&qiov);
-    qemu_io_free(buf);
     return ret;
 }
 
@@ -1035,13 +1068,14 @@ static void write_help(void)
 " filled with a set pattern (0xcdcdcdcd).\n"
 " -b, -- write to the VM state rather than the virtual disk\n"
 " -c, -- write compressed data with blk_write_compressed\n"
+" -C, -- report statistics in a machine parsable format\n"
 " -f, -- use Force Unit Access semantics\n"
 " -n, -- with -z, don't allow slow fallback\n"
 " -p, -- ignored for backwards compatibility\n"
 " -P, -- use different pattern to fill file\n"
+" -q, -- quiet mode, do not show I/O statistics\n"
+" -r, -- register I/O buffer\n"
 " -s, -- use a pattern file to fill the write buffer\n"
-" -C, -- report statistics in a machine parsable format\n"
-" -q, -- quiet mode, do not show I/O statistics\n"
 " -u, -- with -z, allow unmapping\n"
 " -z, -- write zeroes using blk_co_pwrite_zeroes\n"
 "\n");
@@ -1056,7 +1090,7 @@ static const cmdinfo_t write_cmd = {
     .perm       = BLK_PERM_WRITE,
     .argmin     = 2,
     .argmax     = -1,
-    .args       = "[-bcCfnquz] [-P pattern | -s source_file] off len",
+    .args       = "[-bcCfnqruz] [-P pattern | -s source_file] off len",
     .oneline    = "writes a number of bytes at a specified offset",
     .help       = write_help,
 };
@@ -1076,7 +1110,7 @@ static int write_f(BlockBackend *blk, int argc, char **argv)
     int pattern = 0xcd;
     const char *file_name = NULL;
 
-    while ((c = getopt(argc, argv, "bcCfnpP:qs:uz")) != -1) {
+    while ((c = getopt(argc, argv, "bcCfnpP:qrs:uz")) != -1) {
         switch (c) {
         case 'b':
             bflag = true;
@@ -1106,6 +1140,9 @@ static int write_f(BlockBackend *blk, int argc, char **argv)
         case 'q':
             qflag = true;
             break;
+        case 'r':
+            flags |= BDRV_REQ_REGISTERED_BUF;
+            break;
         case 's':
             sflag = true;
             file_name = optarg;
@@ -1185,14 +1222,21 @@ static int write_f(BlockBackend *blk, int argc, char **argv)
         }
     }
 
-    if (!zflag) {
+    if (zflag) {
+        if (flags & BDRV_REQ_REGISTERED_BUF) {
+            printf("cannot combine zero write with register I/O buffer\n");
+            return -EINVAL;
+        }
+    } else {
         if (sflag) {
-            buf = qemu_io_alloc_from_file(blk, count, file_name);
+            buf = qemu_io_alloc_from_file(blk, count, file_name,
+                                          flags & BDRV_REQ_REGISTERED_BUF);
             if (!buf) {
                 return -EINVAL;
             }
         } else {
-            buf = qemu_io_alloc(blk, count, pattern);
+            buf = qemu_io_alloc(blk, count, pattern,
+                                flags & BDRV_REQ_REGISTERED_BUF);
         }
     }
 
@@ -1226,7 +1270,7 @@ static int write_f(BlockBackend *blk, int argc, char **argv)
 
 out:
     if (!zflag) {
-        qemu_io_free(buf);
+        qemu_io_free(blk, buf, count, flags & BDRV_REQ_REGISTERED_BUF);
     }
     return ret;
 }
@@ -1243,10 +1287,11 @@ writev_help(void)
 "\n"
 " Writes into a segment of the currently open file, using a buffer\n"
 " filled with a set pattern (0xcdcdcdcd).\n"
-" -P, -- use different pattern to fill file\n"
 " -C, -- report statistics in a machine parsable format\n"
 " -f, -- use Force Unit Access semantics\n"
+" -P, -- use different pattern to fill file\n"
 " -q, -- quiet mode, do not show I/O statistics\n"
+" -r, -- register I/O buffer\n"
 "\n");
 }
 
@@ -1258,7 +1303,7 @@ static const cmdinfo_t writev_cmd = {
     .perm       = BLK_PERM_WRITE,
     .argmin     = 2,
     .argmax     = -1,
-    .args       = "[-Cfq] [-P pattern] off len [len..]",
+    .args       = "[-Cfqr] [-P pattern] off len [len..]",
     .oneline    = "writes a number of bytes at a specified offset",
     .help       = writev_help,
 };
@@ -1277,7 +1322,7 @@ static int writev_f(BlockBackend *blk, int argc, char **argv)
     int pattern = 0xcd;
     QEMUIOVector qiov;
 
-    while ((c = getopt(argc, argv, "CfqP:")) != -1) {
+    while ((c = getopt(argc, argv, "CfP:qr")) != -1) {
         switch (c) {
         case 'C':
             Cflag = true;
@@ -1288,6 +1333,9 @@ static int writev_f(BlockBackend *blk, int argc, char **argv)
         case 'q':
             qflag = true;
             break;
+        case 'r':
+            flags |= BDRV_REQ_REGISTERED_BUF;
+            break;
         case 'P':
             pattern = parse_pattern(optarg);
             if (pattern < 0) {
@@ -1313,7 +1361,8 @@ static int writev_f(BlockBackend *blk, int argc, char **argv)
     optind++;
 
     nr_iov = argc - optind;
-    buf = create_iovec(blk, &qiov, &argv[optind], nr_iov, pattern);
+    buf = create_iovec(blk, &qiov, &argv[optind], nr_iov, pattern,
+                       flags & BDRV_REQ_REGISTERED_BUF);
     if (buf == NULL) {
         return -EINVAL;
     }
@@ -1338,8 +1387,8 @@ static int writev_f(BlockBackend *blk, int argc, char **argv)
     t2 = tsub(t2, t1);
     print_report("wrote", &t2, offset, qiov.size, total, cnt, Cflag);
 out:
+    qemu_io_free(blk, buf, qiov.size, flags & BDRV_REQ_REGISTERED_BUF);
     qemu_iovec_destroy(&qiov);
-    qemu_io_free(buf);
     return ret;
 }
 
@@ -1355,6 +1404,7 @@ struct aio_ctx {
     bool zflag;
     BlockAcctCookie acct;
     int pattern;
+    BdrvRequestFlags flags;
     struct timespec t1;
 };
 
@@ -1384,8 +1434,9 @@ static void aio_write_done(void *opaque, int ret)
                  ctx->qiov.size, 1, ctx->Cflag);
 out:
     if (!ctx->zflag) {
-        qemu_io_free(ctx->buf);
         qemu_iovec_destroy(&ctx->qiov);
+        qemu_io_free(ctx->blk, ctx->buf, ctx->qiov.size,
+                     ctx->flags & BDRV_REQ_REGISTERED_BUF);
     }
     g_free(ctx);
 }
@@ -1429,7 +1480,8 @@ static void aio_read_done(void *opaque, int ret)
     print_report("read", &t2, ctx->offset, ctx->qiov.size,
                  ctx->qiov.size, 1, ctx->Cflag);
 out:
-    qemu_io_free(ctx->buf);
+    qemu_io_free(ctx->blk, ctx->buf, ctx->qiov.size,
+                 ctx->flags & BDRV_REQ_REGISTERED_BUF);
     qemu_iovec_destroy(&ctx->qiov);
     g_free(ctx);
 }
@@ -1451,10 +1503,11 @@ static void aio_read_help(void)
 " considered successful once the request is submitted, independently\n"
 " of potential I/O errors or pattern mismatches.\n"
 " -C, -- report statistics in a machine parsable format\n"
-" -P, -- use a pattern to verify read data\n"
 " -i, -- treat request as invalid, for exercising stats\n"
-" -v, -- dump buffer to standard output\n"
+" -P, -- use a pattern to verify read data\n"
 " -q, -- quiet mode, do not show I/O statistics\n"
+" -r, -- register I/O buffer\n"
+" -v, -- dump buffer to standard output\n"
 "\n");
 }
 
@@ -1465,7 +1518,7 @@ static const cmdinfo_t aio_read_cmd = {
     .cfunc      = aio_read_f,
     .argmin     = 2,
     .argmax     = -1,
-    .args       = "[-Ciqv] [-P pattern] off len [len..]",
+    .args       = "[-Ciqrv] [-P pattern] off len [len..]",
     .oneline    = "asynchronously reads a number of bytes",
     .help       = aio_read_help,
 };
@@ -1476,7 +1529,7 @@ static int aio_read_f(BlockBackend *blk, int argc, char **argv)
     struct aio_ctx *ctx = g_new0(struct aio_ctx, 1);
 
     ctx->blk = blk;
-    while ((c = getopt(argc, argv, "CP:iqv")) != -1) {
+    while ((c = getopt(argc, argv, "CiP:qrv")) != -1) {
         switch (c) {
         case 'C':
             ctx->Cflag = true;
@@ -1497,6 +1550,9 @@ static int aio_read_f(BlockBackend *blk, int argc, char **argv)
         case 'q':
             ctx->qflag = true;
             break;
+        case 'r':
+            ctx->flags |= BDRV_REQ_REGISTERED_BUF;
+            break;
         case 'v':
             ctx->vflag = true;
             break;
@@ -1523,7 +1579,8 @@ static int aio_read_f(BlockBackend *blk, int argc, char **argv)
     optind++;
 
     nr_iov = argc - optind;
-    ctx->buf = create_iovec(blk, &ctx->qiov, &argv[optind], nr_iov, 0xab);
+    ctx->buf = create_iovec(blk, &ctx->qiov, &argv[optind], nr_iov, 0xab,
+                            ctx->flags & BDRV_REQ_REGISTERED_BUF);
     if (ctx->buf == NULL) {
         block_acct_invalid(blk_get_stats(blk), BLOCK_ACCT_READ);
         g_free(ctx);
@@ -1533,7 +1590,8 @@ static int aio_read_f(BlockBackend *blk, int argc, char **argv)
     clock_gettime(CLOCK_MONOTONIC, &ctx->t1);
     block_acct_start(blk_get_stats(blk), &ctx->acct, ctx->qiov.size,
                      BLOCK_ACCT_READ);
-    blk_aio_preadv(blk, ctx->offset, &ctx->qiov, 0, aio_read_done, ctx);
+    blk_aio_preadv(blk, ctx->offset, &ctx->qiov, ctx->flags, aio_read_done,
+                   ctx);
     return 0;
 }
 
@@ -1554,11 +1612,12 @@ static void aio_write_help(void)
 " Note that due to its asynchronous nature, this command will be\n"
 " considered successful once the request is submitted, independently\n"
 " of potential I/O errors or pattern mismatches.\n"
-" -P, -- use different pattern to fill file\n"
 " -C, -- report statistics in a machine parsable format\n"
 " -f, -- use Force Unit Access semantics\n"
 " -i, -- treat request as invalid, for exercising stats\n"
+" -P, -- use different pattern to fill file\n"
 " -q, -- quiet mode, do not show I/O statistics\n"
+" -r, -- register I/O buffer\n"
 " -u, -- with -z, allow unmapping\n"
 " -z, -- write zeroes using blk_aio_pwrite_zeroes\n"
 "\n");
@@ -1572,7 +1631,7 @@ static const cmdinfo_t aio_write_cmd = {
     .perm       = BLK_PERM_WRITE,
     .argmin     = 2,
     .argmax     = -1,
-    .args       = "[-Cfiquz] [-P pattern] off len [len..]",
+    .args       = "[-Cfiqruz] [-P pattern] off len [len..]",
     .oneline    = "asynchronously writes a number of bytes",
     .help       = aio_write_help,
 };
@@ -1582,22 +1641,24 @@ static int aio_write_f(BlockBackend *blk, int argc, char **argv)
     int nr_iov, c;
     int pattern = 0xcd;
     struct aio_ctx *ctx = g_new0(struct aio_ctx, 1);
-    BdrvRequestFlags flags = 0;
 
     ctx->blk = blk;
-    while ((c = getopt(argc, argv, "CfiqP:uz")) != -1) {
+    while ((c = getopt(argc, argv, "CfiP:qruz")) != -1) {
         switch (c) {
         case 'C':
             ctx->Cflag = true;
             break;
         case 'f':
-            flags |= BDRV_REQ_FUA;
+            ctx->flags |= BDRV_REQ_FUA;
             break;
         case 'q':
             ctx->qflag = true;
             break;
+        case 'r':
+            ctx->flags |= BDRV_REQ_REGISTERED_BUF;
+            break;
         case 'u':
-            flags |= BDRV_REQ_MAY_UNMAP;
+            ctx->flags |= BDRV_REQ_MAY_UNMAP;
             break;
         case 'P':
             pattern = parse_pattern(optarg);
@@ -1633,7 +1694,7 @@ static int aio_write_f(BlockBackend *blk, int argc, char **argv)
         return -EINVAL;
     }
 
-    if ((flags & BDRV_REQ_MAY_UNMAP) && !ctx->zflag) {
+    if ((ctx->flags & BDRV_REQ_MAY_UNMAP) && !ctx->zflag) {
         printf("-u requires -z to be specified\n");
         g_free(ctx);
         return -EINVAL;
@@ -1663,12 +1724,12 @@ static int aio_write_f(BlockBackend *blk, int argc, char **argv)
         }
 
         ctx->qiov.size = count;
-        blk_aio_pwrite_zeroes(blk, ctx->offset, count, flags, aio_write_done,
-                              ctx);
+        blk_aio_pwrite_zeroes(blk, ctx->offset, count, ctx->flags,
+                              aio_write_done, ctx);
     } else {
         nr_iov = argc - optind;
         ctx->buf = create_iovec(blk, &ctx->qiov, &argv[optind], nr_iov,
-                                pattern);
+                                pattern, ctx->flags & BDRV_REQ_REGISTERED_BUF);
         if (ctx->buf == NULL) {
             block_acct_invalid(blk_get_stats(blk), BLOCK_ACCT_WRITE);
             g_free(ctx);
@@ -1679,8 +1740,8 @@ static int aio_write_f(BlockBackend *blk, int argc, char **argv)
         block_acct_start(blk_get_stats(blk), &ctx->acct, ctx->qiov.size,
                          BLOCK_ACCT_WRITE);
 
-        blk_aio_pwritev(blk, ctx->offset, &ctx->qiov, flags, aio_write_done,
-                        ctx);
+        blk_aio_pwritev(blk, ctx->offset, &ctx->qiov, ctx->flags,
+                        aio_write_done, ctx);
     }
 
     return 0;
-- 
2.39.1

Re: [PATCH v3 3/4] qemu-io: add -r option to register I/O buffer

[Hanna Czenczek]

On 01.02.23 16:27, Stefan Hajnoczi wrote:
> The blk_register_buf() API is an optimization hint that allows some
> block drivers to avoid I/O buffer housekeeping or bounce buffers.
>
> Add an -r option to register the I/O buffer so that qemu-io can be used
> to test the blk_register_buf() API. The next commit will add a test that
> uses the new option.
>
> Reviewed-by: Eric Blake <eblake@redhat.com>
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
>   qemu-io-cmds.c | 167 +++++++++++++++++++++++++++++++++----------------
>   1 file changed, 114 insertions(+), 53 deletions(-)
>
> diff --git a/qemu-io-cmds.c b/qemu-io-cmds.c
> index c0125d14c0..4b8dbef36d 100644
> --- a/qemu-io-cmds.c
> +++ b/qemu-io-cmds.c

[...]

> @@ -347,17 +348,24 @@ static void *qemu_io_alloc(BlockBackend *blk, size_t len, int pattern)
>       }
>       buf = blk_blockalign(blk, len);
>       memset(buf, pattern, len);
> +    if (register_buf) {
> +        blk_register_buf(blk, buf, len, &error_abort);
> +    }
>       if (qemuio_misalign) {
>           buf += MISALIGN_OFFSET;
>       }
>       return buf;
>   }
>   
> -static void qemu_io_free(void *p)
> +static void qemu_io_free(BlockBackend *blk, void *p, size_t len,
> +                         bool unregister_buf)
>   {
>       if (qemuio_misalign) {
>           p -= MISALIGN_OFFSET;
>       }
> +    if (unregister_buf) {
> +        blk_unregister_buf(blk, p, len);

If `qemuio_misalign` is set, we must also increase `len` by 
`MISALIGN_OFFSET`, I think, or it won’t match what’s been used in 
`qemu_io_alloc()`.

> +    }
>       qemu_vfree(p);
>   }

[...]

> @@ -414,6 +423,10 @@ static void *qemu_io_alloc_from_file(BlockBackend *blk, size_t len,
>       fclose(f);
>       f = NULL;
>   
> +    if (register_buf) {
> +        blk_register_buf(blk, buf_origin, len, &error_abort);

`qemu_io_alloc()` registers the buffer before `MISALIGN_OFFSET` is/might 
be applied, and `qemu_io_free()` assumes this is the case (the buffer to 
be unregistered is passed after the offset has been subtracted again).  
Here, however, the offset has already been applied, so there’ll be a 
mismatch with `blk_unregister_buf()` when `qemu_io_free()` is called 
(and `qemuio_misalign` is set).

> +    }
> +
>       if (len > pattern_len) {
>           len -= pattern_len;
>           buf += pattern_len;

[...]

> @@ -750,6 +768,7 @@ static int read_f(BlockBackend *blk, int argc, char **argv)
>       int64_t total = 0;
>       int pattern = 0;
>       int64_t pattern_offset = 0, pattern_count = 0;
> +    BdrvRequestFlags flags = 0;
>   
>       while ((c = getopt(argc, argv, "bCl:pP:qs:v")) != -1) {

I think we’ll need the "r" here.

>           switch (c) {

[...]

> @@ -1384,8 +1434,9 @@ static void aio_write_done(void *opaque, int ret)
>                    ctx->qiov.size, 1, ctx->Cflag);
>   out:
>       if (!ctx->zflag) {
> -        qemu_io_free(ctx->buf);
>           qemu_iovec_destroy(&ctx->qiov);
> +        qemu_io_free(ctx->blk, ctx->buf, ctx->qiov.size,
> +                     ctx->flags & BDRV_REQ_REGISTERED_BUF);

So far in this patch, you’ve always swapped the existing 
qemu_iovec_destroy(); qemu_io_free() combination to qemu_io_free(); 
qemu_iovec_destroy().  I think that is correct because 
qemu_iovec_destroy() overwrites the qiov by 0, so that accessing 
qiov.size will then read 0, regardless of what it was before.

Here, you’re swapping it the other way around, which means that 
`ctx->qiov.size` will read 0 when `qemu_io_free()` is called, which 
seems wrong.

>       }
>       g_free(ctx);
>   }

[...]

> @@ -1663,12 +1724,12 @@ static int aio_write_f(BlockBackend *blk, int argc, char **argv)
>           }
>   
>           ctx->qiov.size = count;
> -        blk_aio_pwrite_zeroes(blk, ctx->offset, count, flags, aio_write_done,
> -                              ctx);
> +        blk_aio_pwrite_zeroes(blk, ctx->offset, count, ctx->flags,
> +                              aio_write_done, ctx);

write_f() emits an error when -r is used together with -z – why doesn’t 
this function, too?  (Or, alternatively, why does write_f()?  Maybe we 
want to check what happens when you call a zero-writing function with 
that flag.  Or we don’t.)

Hanna

>       } else {
>           nr_iov = argc - optind;
>           ctx->buf = create_iovec(blk, &ctx->qiov, &argv[optind], nr_iov,
> -                                pattern);
> +                                pattern, ctx->flags & BDRV_REQ_REGISTERED_BUF);
>           if (ctx->buf == NULL) {
>               block_acct_invalid(blk_get_stats(blk), BLOCK_ACCT_WRITE);
>               g_free(ctx);

Re: [PATCH v3 3/4] qemu-io: add -r option to register I/O buffer

[Stefan Hajnoczi]

[-- Attachment #1: Type: text/plain, Size: 4866 bytes --]

On Tue, Feb 07, 2023 at 12:47:06PM +0100, Hanna Czenczek wrote:
> On 01.02.23 16:27, Stefan Hajnoczi wrote:
> > The blk_register_buf() API is an optimization hint that allows some
> > block drivers to avoid I/O buffer housekeeping or bounce buffers.
> > 
> > Add an -r option to register the I/O buffer so that qemu-io can be used
> > to test the blk_register_buf() API. The next commit will add a test that
> > uses the new option.
> > 
> > Reviewed-by: Eric Blake <eblake@redhat.com>
> > Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> > ---
> >   qemu-io-cmds.c | 167 +++++++++++++++++++++++++++++++++----------------
> >   1 file changed, 114 insertions(+), 53 deletions(-)
> > 
> > diff --git a/qemu-io-cmds.c b/qemu-io-cmds.c
> > index c0125d14c0..4b8dbef36d 100644
> > --- a/qemu-io-cmds.c
> > +++ b/qemu-io-cmds.c
> 
> [...]
> 
> > @@ -347,17 +348,24 @@ static void *qemu_io_alloc(BlockBackend *blk, size_t len, int pattern)
> >       }
> >       buf = blk_blockalign(blk, len);
> >       memset(buf, pattern, len);
> > +    if (register_buf) {
> > +        blk_register_buf(blk, buf, len, &error_abort);
> > +    }
> >       if (qemuio_misalign) {
> >           buf += MISALIGN_OFFSET;
> >       }
> >       return buf;
> >   }
> > -static void qemu_io_free(void *p)
> > +static void qemu_io_free(BlockBackend *blk, void *p, size_t len,
> > +                         bool unregister_buf)
> >   {
> >       if (qemuio_misalign) {
> >           p -= MISALIGN_OFFSET;
> >       }
> > +    if (unregister_buf) {
> > +        blk_unregister_buf(blk, p, len);
> 
> If `qemuio_misalign` is set, we must also increase `len` by
> `MISALIGN_OFFSET`, I think, or it won’t match what’s been used in
> `qemu_io_alloc()`.

Good catch, thank you!

> 
> > +    }
> >       qemu_vfree(p);
> >   }
> 
> [...]
> 
> > @@ -414,6 +423,10 @@ static void *qemu_io_alloc_from_file(BlockBackend *blk, size_t len,
> >       fclose(f);
> >       f = NULL;
> > +    if (register_buf) {
> > +        blk_register_buf(blk, buf_origin, len, &error_abort);
> 
> `qemu_io_alloc()` registers the buffer before `MISALIGN_OFFSET` is/might be
> applied, and `qemu_io_free()` assumes this is the case (the buffer to be
> unregistered is passed after the offset has been subtracted again).  Here,
> however, the offset has already been applied, so there’ll be a mismatch with
> `blk_unregister_buf()` when `qemu_io_free()` is called (and
> `qemuio_misalign` is set).
> 
> > +    }
> > +
> >       if (len > pattern_len) {
> >           len -= pattern_len;
> >           buf += pattern_len;
> 
> [...]
> 
> > @@ -750,6 +768,7 @@ static int read_f(BlockBackend *blk, int argc, char **argv)
> >       int64_t total = 0;
> >       int pattern = 0;
> >       int64_t pattern_offset = 0, pattern_count = 0;
> > +    BdrvRequestFlags flags = 0;
> >       while ((c = getopt(argc, argv, "bCl:pP:qs:v")) != -1) {
> 
> I think we’ll need the "r" here.

Oops, thanks!

> 
> >           switch (c) {
> 
> [...]
> 
> > @@ -1384,8 +1434,9 @@ static void aio_write_done(void *opaque, int ret)
> >                    ctx->qiov.size, 1, ctx->Cflag);
> >   out:
> >       if (!ctx->zflag) {
> > -        qemu_io_free(ctx->buf);
> >           qemu_iovec_destroy(&ctx->qiov);
> > +        qemu_io_free(ctx->blk, ctx->buf, ctx->qiov.size,
> > +                     ctx->flags & BDRV_REQ_REGISTERED_BUF);
> 
> So far in this patch, you’ve always swapped the existing
> qemu_iovec_destroy(); qemu_io_free() combination to qemu_io_free();
> qemu_iovec_destroy().  I think that is correct because qemu_iovec_destroy()
> overwrites the qiov by 0, so that accessing qiov.size will then read 0,
> regardless of what it was before.
> 
> Here, you’re swapping it the other way around, which means that
> `ctx->qiov.size` will read 0 when `qemu_io_free()` is called, which seems
> wrong.

Yes, you're right. I will reverse the order here.

> 
> >       }
> >       g_free(ctx);
> >   }
> 
> [...]
> 
> > @@ -1663,12 +1724,12 @@ static int aio_write_f(BlockBackend *blk, int argc, char **argv)
> >           }
> >           ctx->qiov.size = count;
> > -        blk_aio_pwrite_zeroes(blk, ctx->offset, count, flags, aio_write_done,
> > -                              ctx);
> > +        blk_aio_pwrite_zeroes(blk, ctx->offset, count, ctx->flags,
> > +                              aio_write_done, ctx);
> 
> write_f() emits an error when -r is used together with -z – why doesn’t this
> function, too?  (Or, alternatively, why does write_f()?  Maybe we want to
> check what happens when you call a zero-writing function with that flag.  Or
> we don’t.)

I added an explicit check in write_f() and forgot to add the same check
to aio_write_f(). Will fix.

Stefan

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 488 bytes --]

[PATCH v3 4/4] iotests/detect-zeroes-registered-buf: add new test

[Stefan Hajnoczi]

This regression test demonstrates that detect-zeroes works with
registered buffers. Bug details:
https://gitlab.com/qemu-project/qemu/-/issues/1404

Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 .../tests/detect-zeroes-registered-buf        | 58 +++++++++++++++++++
 .../tests/detect-zeroes-registered-buf.out    |  7 +++
 2 files changed, 65 insertions(+)
 create mode 100755 tests/qemu-iotests/tests/detect-zeroes-registered-buf
 create mode 100644 tests/qemu-iotests/tests/detect-zeroes-registered-buf.out

diff --git a/tests/qemu-iotests/tests/detect-zeroes-registered-buf b/tests/qemu-iotests/tests/detect-zeroes-registered-buf
new file mode 100755
index 0000000000..edb5f2cee5
--- /dev/null
+++ b/tests/qemu-iotests/tests/detect-zeroes-registered-buf
@@ -0,0 +1,58 @@
+#!/usr/bin/env bash
+# group: rw auto quick
+#
+# Check that detect-zeroes=unmap works on writes with registered I/O buffers.
+# This is a regression test for
+# https://gitlab.com/qemu-project/qemu/-/issues/1404 where I/O requests failed
+# unexpectedly.
+#
+# Copyright Red Hat
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+#
+
+# creator
+owner=stefanha@redhat.com
+
+seq=`basename $0`
+echo "QA output created by $seq"
+
+status=1	# failure is the default!
+
+_cleanup()
+{
+	_cleanup_test_img
+}
+trap "_cleanup; exit \$status" 0 1 2 3 15
+
+# get standard environment, filters and checks
+cd ..
+. ./common.rc
+. ./common.filter
+
+_supported_fmt qcow2
+_supported_proto generic
+
+size=128M
+_make_test_img $size
+IMGSPEC="driver=$IMGFMT,file.filename=$TEST_IMG,discard=unmap,detect-zeroes=unmap"
+
+echo
+echo "== writing zero buffer to image =="
+QEMU_IO_OPTIONS="$QEMU_IO_OPTIONS_NO_FMT" $QEMU_IO -c "write -r -P 0 0 4k" --image-opts "$IMGSPEC" | _filter_qemu_io
+
+# success, all done
+echo "*** done"
+rm -f $seq.full
+status=0
diff --git a/tests/qemu-iotests/tests/detect-zeroes-registered-buf.out b/tests/qemu-iotests/tests/detect-zeroes-registered-buf.out
new file mode 100644
index 0000000000..42c56fcc8d
--- /dev/null
+++ b/tests/qemu-iotests/tests/detect-zeroes-registered-buf.out
@@ -0,0 +1,7 @@
+QA output created by detect-zeroes-registered-buf
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728
+
+== writing zero buffer to image ==
+wrote 4096/4096 bytes at offset 0
+4 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+*** done
-- 
2.39.1

Re: [PATCH v3 4/4] iotests/detect-zeroes-registered-buf: add new test

[Hanna Czenczek]

On 01.02.23 16:27, Stefan Hajnoczi wrote:
> This regression test demonstrates that detect-zeroes works with
> registered buffers. Bug details:
> https://gitlab.com/qemu-project/qemu/-/issues/1404
>
> Reviewed-by: Eric Blake <eblake@redhat.com>
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
>   .../tests/detect-zeroes-registered-buf        | 58 +++++++++++++++++++
>   .../tests/detect-zeroes-registered-buf.out    |  7 +++
>   2 files changed, 65 insertions(+)
>   create mode 100755 tests/qemu-iotests/tests/detect-zeroes-registered-buf
>   create mode 100644 tests/qemu-iotests/tests/detect-zeroes-registered-buf.out

Reviewed-by: Hanna Czenczek <hreitz@redhat.com>

Re: [PATCH v3 0/4] block: fix detect-zeroes= with BDRV_REQ_REGISTERED_BUF

[Stefan Hajnoczi]

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On Wed, Feb 01, 2023 at 10:27:47AM -0500, Stefan Hajnoczi wrote:
> v3:
> - Restore alphabetical order in getopt strings [Eric]
> v2:
> - Add comment explaining unbalanced error code path in
>   qemu_io_alloc_from_file() [Eric]
> - List options alphabetically in help output [Eric]
> - Add Tested-by/Reviewed-by
> - CC qemu-stable on the fix
> 
> The first patch fixes a regression in QEMU 7.2 where detect-zeroes breaks with
> virtio-blk devices due to a BDRV_REQ_REGISTERED_BUF bug. Details of the
> regression can be found here:
> https://gitlab.com/qemu-project/qemu/-/issues/1404
> 
> The remaining patches add a regression test that will protect this code path in
> the future. The qemu-io command is extended with the new -r option that calls
> blk_register_buf(). This allows a qemu-iotests test case to trigger the same
> bug as virtio-blk.
> 
> Stefan Hajnoczi (4):
>   block: fix detect-zeroes= with BDRV_REQ_REGISTERED_BUF
>   qemu-io: use BdrvRequestFlags instead of int
>   qemu-io: add -r option to register I/O buffer
>   iotests/detect-zeroes-registered-buf: add new test
> 
>  block/io.c                                    |   3 +
>  qemu-io-cmds.c                                | 180 ++++++++++++------
>  .../tests/detect-zeroes-registered-buf        |  58 ++++++
>  .../tests/detect-zeroes-registered-buf.out    |   7 +
>  4 files changed, 189 insertions(+), 59 deletions(-)
>  create mode 100755 tests/qemu-iotests/tests/detect-zeroes-registered-buf
>  create mode 100644 tests/qemu-iotests/tests/detect-zeroes-registered-buf.out

Hi Kevin and Hanna,
Would you like to review this or should I go ahead and merge it?

Stefan

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