[Qemu-devel] [RFC PATCH v4 0/4] qemu-img: add preallocation=full

[Qemu-devel] [RFC PATCH v4 0/4] qemu-img: add preallocation=full

[Hu Tao]

This series implements full image preallocation to create a non-sparse image
file at creation time, both for raw and qcow2 format. The purpose is to avoid
performance deterioration of the guest cause by sparse image.

v4:  - remove bdrv_preallocate and make preallocation a bdrv_create_file option
     - prealloc_mode -> PreallocMode and add it to QAPI
     - fix return value in raw_preallocate2

Hu Tao (4):
  qapi: introduce PreallocMode
  raw,qcow2: don't convert file size to sector size
  raw-posix: Add full image preallocation option
  qcow2: Add full image preallocation option

 block/qcow2.c     | 64 +++++++++++++++++++++++++++++++++++++++++++++----------
 block/raw-posix.c | 50 +++++++++++++++++++++++++++++++++++++++++--
 qapi-schema.json  | 12 +++++++++++
 3 files changed, 113 insertions(+), 13 deletions(-)

-- 
1.7.11.7

[Qemu-devel] [RFC PATCH v4 1/4] qapi: introduce PreallocMode

[Hu Tao]

This patch prepares for the subsequent patches.

Signed-off-by: Hu Tao <hutao@cn.fujitsu.com>
---
 block/qcow2.c    |  8 ++++----
 qapi-schema.json | 12 ++++++++++++
 2 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/block/qcow2.c b/block/qcow2.c
index f29aa88..729dac6 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -1444,7 +1444,7 @@ static int preallocate(BlockDriverState *bs)
 
 static int qcow2_create2(const char *filename, int64_t total_size,
                          const char *backing_file, const char *backing_format,
-                         int flags, size_t cluster_size, int prealloc,
+                         int flags, size_t cluster_size, PreallocMode prealloc,
                          QEMUOptionParameter *options, int version,
                          Error **errp)
 {
@@ -1614,7 +1614,7 @@ static int qcow2_create(const char *filename, QEMUOptionParameter *options,
     uint64_t sectors = 0;
     int flags = 0;
     size_t cluster_size = DEFAULT_CLUSTER_SIZE;
-    int prealloc = 0;
+    PreallocMode prealloc = PREALLOC_MODE_OFF;
     int version = 3;
     Error *local_err = NULL;
     int ret;
@@ -1635,9 +1635,9 @@ static int qcow2_create(const char *filename, QEMUOptionParameter *options,
             }
         } else if (!strcmp(options->name, BLOCK_OPT_PREALLOC)) {
             if (!options->value.s || !strcmp(options->value.s, "off")) {
-                prealloc = 0;
+                prealloc = PREALLOC_MODE_OFF;
             } else if (!strcmp(options->value.s, "metadata")) {
-                prealloc = 1;
+                prealloc = PREALLOC_MODE_METADATA;
             } else {
                 error_setg(errp, "Invalid preallocation mode: '%s'",
                            options->value.s);
diff --git a/qapi-schema.json b/qapi-schema.json
index c3c939c..64533f1 100644
--- a/qapi-schema.json
+++ b/qapi-schema.json
@@ -4235,3 +4235,15 @@
 # Since: 1.7
 ##
 { 'command': 'blockdev-add', 'data': { 'options': 'BlockdevOptions' } }
+
+##
+# @PreallocMode
+#
+# Preallocation mode of QEMU image file
+#
+# @off: no preallocation
+# @metadata: preallocate only for metadata
+# @full: preallocate all data, including metadata
+##
+{ 'enum': 'PreallocMode',
+  'data': [ 'off', 'metadata', 'full' ] }
-- 
1.7.11.7

[Qemu-devel] [RFC PATCH v4 2/4] raw, qcow2: don't convert file size to sector size

[Hu Tao]

and avoid convert it back later.

Signed-off-by: Hu Tao <hutao@cn.fujitsu.com>
---
 block/qcow2.c     | 8 ++++----
 block/raw-posix.c | 4 ++--
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/block/qcow2.c b/block/qcow2.c
index 729dac6..f0a8d87 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -1561,7 +1561,7 @@ static int qcow2_create2(const char *filename, int64_t total_size,
     }
 
     /* Okay, now that we have a valid image, let's give it the right size */
-    ret = bdrv_truncate(bs, total_size * BDRV_SECTOR_SIZE);
+    ret = bdrv_truncate(bs, total_size);
     if (ret < 0) {
         error_setg_errno(errp, -ret, "Could not resize image");
         goto out;
@@ -1611,7 +1611,7 @@ static int qcow2_create(const char *filename, QEMUOptionParameter *options,
 {
     const char *backing_file = NULL;
     const char *backing_fmt = NULL;
-    uint64_t sectors = 0;
+    uint64_t size = 0;
     int flags = 0;
     size_t cluster_size = DEFAULT_CLUSTER_SIZE;
     PreallocMode prealloc = PREALLOC_MODE_OFF;
@@ -1622,7 +1622,7 @@ static int qcow2_create(const char *filename, QEMUOptionParameter *options,
     /* Read out options */
     while (options && options->name) {
         if (!strcmp(options->name, BLOCK_OPT_SIZE)) {
-            sectors = options->value.n / 512;
+            size = options->value.n & BDRV_SECTOR_MASK;
         } else if (!strcmp(options->name, BLOCK_OPT_BACKING_FILE)) {
             backing_file = options->value.s;
         } else if (!strcmp(options->name, BLOCK_OPT_BACKING_FMT)) {
@@ -1673,7 +1673,7 @@ static int qcow2_create(const char *filename, QEMUOptionParameter *options,
         return -EINVAL;
     }
 
-    ret = qcow2_create2(filename, sectors, backing_file, backing_fmt, flags,
+    ret = qcow2_create2(filename, size, backing_file, backing_fmt, flags,
                         cluster_size, prealloc, options, version, &local_err);
     if (error_is_set(&local_err)) {
         error_propagate(errp, local_err);
diff --git a/block/raw-posix.c b/block/raw-posix.c
index 10c6b34..6f6b8c1 100644
--- a/block/raw-posix.c
+++ b/block/raw-posix.c
@@ -1170,7 +1170,7 @@ static int raw_create(const char *filename, QEMUOptionParameter *options,
     /* Read out options */
     while (options && options->name) {
         if (!strcmp(options->name, BLOCK_OPT_SIZE)) {
-            total_size = options->value.n / BDRV_SECTOR_SIZE;
+            total_size = options->value.n & BDRV_SECTOR_MASK;
         }
         options++;
     }
@@ -1181,7 +1181,7 @@ static int raw_create(const char *filename, QEMUOptionParameter *options,
         result = -errno;
         error_setg_errno(errp, -result, "Could not create file");
     } else {
-        if (ftruncate(fd, total_size * BDRV_SECTOR_SIZE) != 0) {
+        if (ftruncate(fd, total_size) != 0) {
             result = -errno;
             error_setg_errno(errp, -result, "Could not resize file");
         }
-- 
1.7.11.7

[Qemu-devel] [RFC PATCH v4 3/4] raw-posix: Add full image preallocation option

[Hu Tao]

This patch adds a new option preallocation for raw format, and implements
full preallocation.

Signed-off-by: Hu Tao <hutao@cn.fujitsu.com>
---
 block/raw-posix.c | 46 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 46 insertions(+)

diff --git a/block/raw-posix.c b/block/raw-posix.c
index 6f6b8c1..a722d27 100644
--- a/block/raw-posix.c
+++ b/block/raw-posix.c
@@ -1160,17 +1160,52 @@ static int64_t raw_get_allocated_file_size(BlockDriverState *bs)
     return (int64_t)st.st_blocks * 512;
 }
 
+#ifdef __linux__
+static int raw_preallocate2(int fd, int64_t offset, int64_t length)
+{
+    int ret = -1;
+
+    ret = fallocate(fd, 0, offset, length);
+    if (ret < 0) {
+        ret = -errno;
+    }
+
+    /* fallback to posix_fallocate() if fallocate() is not supported */
+    if (ret == -ENOSYS || ret == -EOPNOTSUPP) {
+        ret = posix_fallocate(fd, offset, length);
+    }
+
+    return ret;
+}
+#else
+static int raw_preallocate2(int fd, int64_t offset, int64_t length)
+{
+    return posix_fallocate(fd, offset, length);
+}
+#endif
+
 static int raw_create(const char *filename, QEMUOptionParameter *options,
                       Error **errp)
 {
     int fd;
     int result = 0;
     int64_t total_size = 0;
+    PreallocMode prealloc = PREALLOC_MODE_OFF;
 
     /* Read out options */
     while (options && options->name) {
         if (!strcmp(options->name, BLOCK_OPT_SIZE)) {
             total_size = options->value.n & BDRV_SECTOR_MASK;
+        } else if (!strcmp(options->name, BLOCK_OPT_PREALLOC)) {
+            if (!options->value.s || !strcmp(options->value.s, "off")) {
+                prealloc = PREALLOC_MODE_OFF;
+            } else if (!strcmp(options->value.s, "full")) {
+                prealloc = PREALLOC_MODE_FULL;
+            } else {
+                error_setg(errp, "Invalid preallocation mode: '%s'",
+                           options->value.s);
+                return -EINVAL;
+            }
         }
         options++;
     }
@@ -1185,6 +1220,12 @@ static int raw_create(const char *filename, QEMUOptionParameter *options,
             result = -errno;
             error_setg_errno(errp, -result, "Could not resize file");
         }
+        if (prealloc == PREALLOC_MODE_FULL) {
+            result = raw_preallocate2(fd, 0, total_size);
+            if (result != 0)
+                error_setg_errno(errp, -result,
+                                 "Could not preallocate data for the new file");
+        }
         if (qemu_close(fd) != 0) {
             result = -errno;
             error_setg_errno(errp, -result, "Could not close the new file");
@@ -1340,6 +1381,11 @@ static QEMUOptionParameter raw_create_options[] = {
         .type = OPT_SIZE,
         .help = "Virtual disk size"
     },
+    {
+        .name = BLOCK_OPT_PREALLOC,
+        .type = OPT_STRING,
+        .help = "Preallocation mode (allowed values: off, full)"
+    },
     { NULL }
 };
 
-- 
1.7.11.7

Re: [Qemu-devel] [RFC PATCH v4 3/4] raw-posix: Add full image preallocation option

[Stefan Hajnoczi]

On Fri, Dec 27, 2013 at 11:05:53AM +0800, Hu Tao wrote:
> This patch adds a new option preallocation for raw format, and implements
> full preallocation.
> 
> Signed-off-by: Hu Tao <hutao@cn.fujitsu.com>
> ---
>  block/raw-posix.c | 46 ++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 46 insertions(+)
> 
> diff --git a/block/raw-posix.c b/block/raw-posix.c
> index 6f6b8c1..a722d27 100644
> --- a/block/raw-posix.c
> +++ b/block/raw-posix.c
> @@ -1160,17 +1160,52 @@ static int64_t raw_get_allocated_file_size(BlockDriverState *bs)
>      return (int64_t)st.st_blocks * 512;
>  }
>  
> +#ifdef __linux__
> +static int raw_preallocate2(int fd, int64_t offset, int64_t length)

Why is this function called raw_preallocate2()?  Please choose a
descriptive name.

> +{
> +    int ret = -1;
> +
> +    ret = fallocate(fd, 0, offset, length);
> +    if (ret < 0) {
> +        ret = -errno;
> +    }
> +
> +    /* fallback to posix_fallocate() if fallocate() is not supported */
> +    if (ret == -ENOSYS || ret == -EOPNOTSUPP) {
> +        ret = posix_fallocate(fd, offset, length);

>From the posix_fallocate(3) man page:
"posix_fallocate() returns zero on success, or an error number on
failure.  Note that errno is not set."

You need to negate the error number:
if (ret > 0) {
    ret = -ret; /* posix_fallocate(3) returns a positive errno */
}

> +    }
> +
> +    return ret;
> +}
> +#else
> +static int raw_preallocate2(int fd, int64_t offset, int64_t length)
> +{
> +    return posix_fallocate(fd, offset, length);

Same error number problem as above.

> @@ -1185,6 +1220,12 @@ static int raw_create(const char *filename, QEMUOptionParameter *options,
>              result = -errno;
>              error_setg_errno(errp, -result, "Could not resize file");
>          }
> +        if (prealloc == PREALLOC_MODE_FULL) {
> +            result = raw_preallocate2(fd, 0, total_size);

What if ftruncate() failed?  We should not try to fallocate.  Please add
a proper error return path.

> +            if (result != 0)
> +                error_setg_errno(errp, -result,
> +                                 "Could not preallocate data for the new file");

WARNING: braces {} are necessary for all arms of this statement

Please run scripts/checkpatch.pl before submitting patches, it checks
QEMU coding style.

Re: [Qemu-devel] [RFC PATCH v4 3/4] raw-posix: Add full image preallocation option

[Hu Tao]

On Fri, Jan 17, 2014 at 04:25:14PM +0800, Stefan Hajnoczi wrote:
> On Fri, Dec 27, 2013 at 11:05:53AM +0800, Hu Tao wrote:
> > This patch adds a new option preallocation for raw format, and implements
> > full preallocation.
> > 
> > Signed-off-by: Hu Tao <hutao@cn.fujitsu.com>
> > ---
> >  block/raw-posix.c | 46 ++++++++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 46 insertions(+)
> > 
> > diff --git a/block/raw-posix.c b/block/raw-posix.c
> > index 6f6b8c1..a722d27 100644
> > --- a/block/raw-posix.c
> > +++ b/block/raw-posix.c
> > @@ -1160,17 +1160,52 @@ static int64_t raw_get_allocated_file_size(BlockDriverState *bs)
> >      return (int64_t)st.st_blocks * 512;
> >  }
> >  
> > +#ifdef __linux__
> > +static int raw_preallocate2(int fd, int64_t offset, int64_t length)
> 
> Why is this function called raw_preallocate2()?  Please choose a
> descriptive name.

Sure.

> 
> > +{
> > +    int ret = -1;
> > +
> > +    ret = fallocate(fd, 0, offset, length);
> > +    if (ret < 0) {
> > +        ret = -errno;
> > +    }
> > +
> > +    /* fallback to posix_fallocate() if fallocate() is not supported */
> > +    if (ret == -ENOSYS || ret == -EOPNOTSUPP) {
> > +        ret = posix_fallocate(fd, offset, length);
> 
> From the posix_fallocate(3) man page:
> "posix_fallocate() returns zero on success, or an error number on
> failure.  Note that errno is not set."
> 
> You need to negate the error number:
> if (ret > 0) {
>     ret = -ret; /* posix_fallocate(3) returns a positive errno */
> }

Sure.

> 
> > +    }
> > +
> > +    return ret;
> > +}
> > +#else
> > +static int raw_preallocate2(int fd, int64_t offset, int64_t length)
> > +{
> > +    return posix_fallocate(fd, offset, length);
> 
> Same error number problem as above.
> 
> > @@ -1185,6 +1220,12 @@ static int raw_create(const char *filename, QEMUOptionParameter *options,
> >              result = -errno;
> >              error_setg_errno(errp, -result, "Could not resize file");
> >          }
> > +        if (prealloc == PREALLOC_MODE_FULL) {
> > +            result = raw_preallocate2(fd, 0, total_size);
> 
> What if ftruncate() failed?  We should not try to fallocate.  Please add
> a proper error return path.

Sure.

> 
> > +            if (result != 0)
> > +                error_setg_errno(errp, -result,
> > +                                 "Could not preallocate data for the new file");
> 
> WARNING: braces {} are necessary for all arms of this statement
> 
> Please run scripts/checkpatch.pl before submitting patches, it checks
> QEMU coding style.

Thanks!

Re: [Qemu-devel] [RFC PATCH v4 3/4] raw-posix: Add full image preallocation option

[Stefan Hajnoczi]

On Fri, Dec 27, 2013 at 11:05:53AM +0800, Hu Tao wrote:
> diff --git a/block/raw-posix.c b/block/raw-posix.c
> index 6f6b8c1..a722d27 100644
> --- a/block/raw-posix.c
> +++ b/block/raw-posix.c
> @@ -1160,17 +1160,52 @@ static int64_t raw_get_allocated_file_size(BlockDriverState *bs)
>      return (int64_t)st.st_blocks * 512;
>  }
>  
> +#ifdef __linux__
> +static int raw_preallocate2(int fd, int64_t offset, int64_t length)
> +{
> +    int ret = -1;
> +
> +    ret = fallocate(fd, 0, offset, length);
> +    if (ret < 0) {
> +        ret = -errno;
> +    }
> +
> +    /* fallback to posix_fallocate() if fallocate() is not supported */
> +    if (ret == -ENOSYS || ret == -EOPNOTSUPP) {
> +        ret = posix_fallocate(fd, offset, length);
> +    }
> +
> +    return ret;
> +}

Why is this Linux-specific #ifdef necessary?  glibc will try to use the
fallocate(2) system call, if possible.

Stefan

Re: [Qemu-devel] [RFC PATCH v4 3/4] raw-posix: Add full image preallocation option

[Hu Tao]

On Fri, Jan 17, 2014 at 04:56:42PM +0800, Stefan Hajnoczi wrote:
> On Fri, Dec 27, 2013 at 11:05:53AM +0800, Hu Tao wrote:
> > diff --git a/block/raw-posix.c b/block/raw-posix.c
> > index 6f6b8c1..a722d27 100644
> > --- a/block/raw-posix.c
> > +++ b/block/raw-posix.c
> > @@ -1160,17 +1160,52 @@ static int64_t raw_get_allocated_file_size(BlockDriverState *bs)
> >      return (int64_t)st.st_blocks * 512;
> >  }
> >  
> > +#ifdef __linux__
> > +static int raw_preallocate2(int fd, int64_t offset, int64_t length)
> > +{
> > +    int ret = -1;
> > +
> > +    ret = fallocate(fd, 0, offset, length);
> > +    if (ret < 0) {
> > +        ret = -errno;
> > +    }
> > +
> > +    /* fallback to posix_fallocate() if fallocate() is not supported */
> > +    if (ret == -ENOSYS || ret == -EOPNOTSUPP) {
> > +        ret = posix_fallocate(fd, offset, length);
> > +    }
> > +
> > +    return ret;
> > +}
> 
> Why is this Linux-specific #ifdef necessary?  glibc will try to use the
> fallocate(2) system call, if possible.

Fine. I'll drop this.

[Qemu-devel] [RFC PATCH v4 4/4] qcow2: Add full image preallocation option

[Hu Tao]

This adds a preallocation=full mode to qcow2 image creation, which
creates a non-sparse image file.

Signed-off-by: Hu Tao <hutao@cn.fujitsu.com>
---
 block/qcow2.c | 48 +++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 45 insertions(+), 3 deletions(-)

diff --git a/block/qcow2.c b/block/qcow2.c
index f0a8d87..f601089 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -1448,6 +1448,7 @@ static int qcow2_create2(const char *filename, int64_t total_size,
                          QEMUOptionParameter *options, int version,
                          Error **errp)
 {
+    QEMUOptionParameter *alloc_options = NULL;
     /* Calculate cluster_bits */
     int cluster_bits;
     cluster_bits = ffs(cluster_size) - 1;
@@ -1477,16 +1478,53 @@ static int qcow2_create2(const char *filename, int64_t total_size,
     Error *local_err = NULL;
     int ret;
 
+    if (prealloc == PREALLOC_MODE_FULL) {
+        int64_t meta_size = 0;
+        unsigned nrefe, nl2e;
+        BlockDriver *drv;
+
+        drv = bdrv_find_protocol(filename, true);
+        if (drv == NULL) {
+            error_setg(errp, "Could not find protocol for file '%s'", filename);
+            return -ENOENT;
+        }
+
+        alloc_options = append_option_parameters(alloc_options,
+                                                 drv->create_options);
+        alloc_options = append_option_parameters(alloc_options, options);
+
+        /* header: 1 cluster */
+        meta_size += cluster_size;
+        /* total size of refblocks */
+        nrefe = (total_size / cluster_size);
+        nrefe = align_offset(nrefe, cluster_size / sizeof(uint16_t));
+        meta_size += nrefe * sizeof(uint16_t);
+        /* total size of reftables */
+        meta_size += nrefe * sizeof(uint16_t) * sizeof(uint16_t) / cluster_size;
+        /* total size of L2 tables */
+        nl2e = total_size / cluster_size;
+        nl2e = align_offset(nl2e, cluster_size / sizeof(uint64_t));
+        meta_size += nl2e * sizeof(uint64_t);
+        /* total size of L1 tables */
+        meta_size += nl2e * sizeof(uint64_t) * sizeof(uint64_t) / cluster_size;
+
+        set_option_parameter_int(alloc_options, BLOCK_OPT_SIZE,
+                                 total_size + meta_size);
+        set_option_parameter(alloc_options, BLOCK_OPT_PREALLOC, "full");
+
+        options = alloc_options;
+    }
+
     ret = bdrv_create_file(filename, options, &local_err);
     if (ret < 0) {
         error_propagate(errp, local_err);
-        return ret;
+        goto out_options;
     }
 
     ret = bdrv_file_open(&bs, filename, NULL, BDRV_O_RDWR, &local_err);
     if (ret < 0) {
         error_propagate(errp, local_err);
-        return ret;
+        goto out_options;
     }
 
     /* Write the header */
@@ -1603,6 +1641,8 @@ static int qcow2_create2(const char *filename, int64_t total_size,
     ret = 0;
 out:
     bdrv_unref(bs);
+out_options:
+    free_option_parameters(alloc_options);
     return ret;
 }
 
@@ -1638,6 +1678,8 @@ static int qcow2_create(const char *filename, QEMUOptionParameter *options,
                 prealloc = PREALLOC_MODE_OFF;
             } else if (!strcmp(options->value.s, "metadata")) {
                 prealloc = PREALLOC_MODE_METADATA;
+            } else if (!strcmp(options->value.s, "full")) {
+                prealloc = PREALLOC_MODE_FULL;
             } else {
                 error_setg(errp, "Invalid preallocation mode: '%s'",
                            options->value.s);
@@ -2223,7 +2265,7 @@ static QEMUOptionParameter qcow2_create_options[] = {
     {
         .name = BLOCK_OPT_PREALLOC,
         .type = OPT_STRING,
-        .help = "Preallocation mode (allowed values: off, metadata)"
+        .help = "Preallocation mode (allowed values: off, metadata, full)"
     },
     {
         .name = BLOCK_OPT_LAZY_REFCOUNTS,
-- 
1.7.11.7

Re: [Qemu-devel] [RFC PATCH v4 4/4] qcow2: Add full image preallocation option

[Stefan Hajnoczi]

On Fri, Dec 27, 2013 at 11:05:54AM +0800, Hu Tao wrote:

This approach seems okay but the calculation isn't quite right yet.

On Windows an error would be raised since we don't have preallocate=full
support.  That's okay.

> @@ -1477,16 +1478,53 @@ static int qcow2_create2(const char *filename, int64_t total_size,
>      Error *local_err = NULL;
>      int ret;
>  
> +    if (prealloc == PREALLOC_MODE_FULL) {
> +        int64_t meta_size = 0;
> +        unsigned nrefe, nl2e;
> +        BlockDriver *drv;
> +
> +        drv = bdrv_find_protocol(filename, true);
> +        if (drv == NULL) {
> +            error_setg(errp, "Could not find protocol for file '%s'", filename);
> +            return -ENOENT;
> +        }
> +
> +        alloc_options = append_option_parameters(alloc_options,
> +                                                 drv->create_options);
> +        alloc_options = append_option_parameters(alloc_options, options);
> +
> +        /* header: 1 cluster */
> +        meta_size += cluster_size;
> +        /* total size of refblocks */
> +        nrefe = (total_size / cluster_size);
> +        nrefe = align_offset(nrefe, cluster_size / sizeof(uint16_t));
> +        meta_size += nrefe * sizeof(uint16_t);

Every host cluster is reference-counted, including metadata (even
refcount blocks are recursively included).  This calculation is wrong
because it only considers data clusters.

> +        /* total size of reftables */
> +        meta_size += nrefe * sizeof(uint16_t) * sizeof(uint16_t) / cluster_size;

I don't understand this calculation.  The refcount table consists of
contiguous clusters where each element is a 64-bit offset to a refcount
block.

> +        /* total size of L2 tables */
> +        nl2e = total_size / cluster_size;
> +        nl2e = align_offset(nl2e, cluster_size / sizeof(uint64_t));
> +        meta_size += nl2e * sizeof(uint64_t);
> +        /* total size of L1 tables */
> +        meta_size += nl2e * sizeof(uint64_t) * sizeof(uint64_t) / cluster_size;

Another strange calculation.  The L1 table consists of contiguous
clusters where each element is a 64-bit offset to an L1 table.

Re: [Qemu-devel] [RFC PATCH v4 4/4] qcow2: Add full image preallocation option

[Hu Tao]

Stefan, 

On Fri, Jan 17, 2014 at 04:48:16PM +0800, Stefan Hajnoczi wrote:
> On Fri, Dec 27, 2013 at 11:05:54AM +0800, Hu Tao wrote:
> 
> This approach seems okay but the calculation isn't quite right yet.
> 
> On Windows an error would be raised since we don't have preallocate=full
> support.  That's okay.
> 
> > @@ -1477,16 +1478,53 @@ static int qcow2_create2(const char *filename, int64_t total_size,
> >      Error *local_err = NULL;
> >      int ret;
> >  
> > +    if (prealloc == PREALLOC_MODE_FULL) {
> > +        int64_t meta_size = 0;
> > +        unsigned nrefe, nl2e;
> > +        BlockDriver *drv;
> > +
> > +        drv = bdrv_find_protocol(filename, true);
> > +        if (drv == NULL) {
> > +            error_setg(errp, "Could not find protocol for file '%s'", filename);
> > +            return -ENOENT;
> > +        }
> > +
> > +        alloc_options = append_option_parameters(alloc_options,
> > +                                                 drv->create_options);
> > +        alloc_options = append_option_parameters(alloc_options, options);
> > +
> > +        /* header: 1 cluster */
> > +        meta_size += cluster_size;
> > +        /* total size of refblocks */
> > +        nrefe = (total_size / cluster_size);
> > +        nrefe = align_offset(nrefe, cluster_size / sizeof(uint16_t));
> > +        meta_size += nrefe * sizeof(uint16_t);
> 
> Every host cluster is reference-counted, including metadata (even
> refcount blocks are recursively included).  This calculation is wrong
> because it only considers data clusters.

Right. I'll fix this.

> 
> > +        /* total size of reftables */
> > +        meta_size += nrefe * sizeof(uint16_t) * sizeof(uint16_t) / cluster_size;
> 
> I don't understand this calculation.  The refcount table consists of
> contiguous clusters where each element is a 64-bit offset to a refcount
> block.
> 
> > +        /* total size of L2 tables */
> > +        nl2e = total_size / cluster_size;
> > +        nl2e = align_offset(nl2e, cluster_size / sizeof(uint64_t));
> > +        meta_size += nl2e * sizeof(uint64_t);
> > +        /* total size of L1 tables */
> > +        meta_size += nl2e * sizeof(uint64_t) * sizeof(uint64_t) / cluster_size;
> 
> Another strange calculation.  The L1 table consists of contiguous
> clusters where each element is a 64-bit offset to an L1 table.

I guest you mean "...offset to an L2 table" here.

Given the number of total L2 table entries nl2e, the number of L2 tables
is:

  nl2table = nl2e * sizeof(l2e) / cluster_size

because each L1 table entry points to a L2 table, so this is also the
number of L1 table entries. So the total size of L1 tables is:

  l1table_size = nl2table * sizeof(l1e)
               = nl2e * sizeof(l2e) * sizeof(l1e) / cluster_size
               = nl2e * sizeof(uint64_t) * sizeof(uint64_t) / cluster_size

I still can't see what's wrong here. But you're welcome to fix me.


The caculation of reftable size above is wrong because of the two problem
you've pointed out. Thanks!

Re: [Qemu-devel] [RFC PATCH v4 4/4] qcow2: Add full image preallocation option

[Hu Tao]

On Mon, Jan 20, 2014 at 10:16:23AM +0800, Hu Tao wrote:
> Stefan, 
> 
> On Fri, Jan 17, 2014 at 04:48:16PM +0800, Stefan Hajnoczi wrote:
> > On Fri, Dec 27, 2013 at 11:05:54AM +0800, Hu Tao wrote:
> > 
> > This approach seems okay but the calculation isn't quite right yet.
> > 
> > On Windows an error would be raised since we don't have preallocate=full
> > support.  That's okay.
> > 
> > > @@ -1477,16 +1478,53 @@ static int qcow2_create2(const char *filename, int64_t total_size,
> > >      Error *local_err = NULL;
> > >      int ret;
> > >  
> > > +    if (prealloc == PREALLOC_MODE_FULL) {
> > > +        int64_t meta_size = 0;
> > > +        unsigned nrefe, nl2e;
> > > +        BlockDriver *drv;
> > > +
> > > +        drv = bdrv_find_protocol(filename, true);
> > > +        if (drv == NULL) {
> > > +            error_setg(errp, "Could not find protocol for file '%s'", filename);
> > > +            return -ENOENT;
> > > +        }
> > > +
> > > +        alloc_options = append_option_parameters(alloc_options,
> > > +                                                 drv->create_options);
> > > +        alloc_options = append_option_parameters(alloc_options, options);
> > > +
> > > +        /* header: 1 cluster */
> > > +        meta_size += cluster_size;
> > > +        /* total size of refblocks */
> > > +        nrefe = (total_size / cluster_size);
> > > +        nrefe = align_offset(nrefe, cluster_size / sizeof(uint16_t));
> > > +        meta_size += nrefe * sizeof(uint16_t);
> > 
> > Every host cluster is reference-counted, including metadata (even
> > refcount blocks are recursively included).  This calculation is wrong
> > because it only considers data clusters.
> 
> Right. I'll fix this.
> 
> > 
> > > +        /* total size of reftables */
> > > +        meta_size += nrefe * sizeof(uint16_t) * sizeof(uint16_t) / cluster_size;
> > 
> > I don't understand this calculation.  The refcount table consists of
> > contiguous clusters where each element is a 64-bit offset to a refcount
> > block.
> > 
> > > +        /* total size of L2 tables */
> > > +        nl2e = total_size / cluster_size;
> > > +        nl2e = align_offset(nl2e, cluster_size / sizeof(uint64_t));
> > > +        meta_size += nl2e * sizeof(uint64_t);
> > > +        /* total size of L1 tables */
> > > +        meta_size += nl2e * sizeof(uint64_t) * sizeof(uint64_t) / cluster_size;
> > 
> > Another strange calculation.  The L1 table consists of contiguous
> > clusters where each element is a 64-bit offset to an L1 table.
> 
> I guest you mean "...offset to an L2 table" here.
> 
> Given the number of total L2 table entries nl2e, the number of L2 tables
> is:
> 
>   nl2table = nl2e * sizeof(l2e) / cluster_size
> 
> because each L1 table entry points to a L2 table, so this is also the
> number of L1 table entries. So the total size of L1 tables is:
> 
>   l1table_size = nl2table * sizeof(l1e)
>                = nl2e * sizeof(l2e) * sizeof(l1e) / cluster_size
>                = nl2e * sizeof(uint64_t) * sizeof(uint64_t) / cluster_size
> 
> I still can't see what's wrong here. But you're welcome to fix me.

Hi,

Any comments?

-- 
Regards,
Hu Tao

Re: [Qemu-devel] [RFC PATCH v4 0/4] qemu-img: add preallocation=full

[Hu Tao]

ping...

Re: [Qemu-devel] [RFC PATCH v4 0/4] qemu-img: add preallocation=full

[Hu Tao]

ping...

Re: [Qemu-devel] [RFC PATCH v4 0/4] qemu-img: add preallocation=full

[Stefan Hajnoczi]

On Fri, Dec 27, 2013 at 11:05:50AM +0800, Hu Tao wrote:
> This series implements full image preallocation to create a non-sparse image
> file at creation time, both for raw and qcow2 format. The purpose is to avoid
> performance deterioration of the guest cause by sparse image.
> 
> v4:  - remove bdrv_preallocate and make preallocation a bdrv_create_file option
>      - prealloc_mode -> PreallocMode and add it to QAPI
>      - fix return value in raw_preallocate2
> 
> Hu Tao (4):
>   qapi: introduce PreallocMode
>   raw,qcow2: don't convert file size to sector size
>   raw-posix: Add full image preallocation option
>   qcow2: Add full image preallocation option
> 
>  block/qcow2.c     | 64 +++++++++++++++++++++++++++++++++++++++++++++----------
>  block/raw-posix.c | 50 +++++++++++++++++++++++++++++++++++++++++--
>  qapi-schema.json  | 12 +++++++++++
>  3 files changed, 113 insertions(+), 13 deletions(-)

I've thought more about the lack of progress information during
posix_fallocate(3).  Users creating 10s or 100s of GB images may have to
wait for a long time if posix_fallocate(3) is implemented in userspace
(effectively dd if=/dev/zero of=vm.img).

But I think adding preallocate=full is a good starting point.  Modern
file systems implement it efficiently so the wait time should be
negligible.  If creating images takes too long we could consider a
fancier interface later.

I left comments on specific patches.