[v3,04/16] qemu-img: Expose PreallocMode for resizing
diff mbox

Message ID 20170526165518.7580-5-mreitz@redhat.com
State New
Headers show

Commit Message

Max Reitz May 26, 2017, 4:55 p.m. UTC
Add a --preallocation command line option to qemu-img resize which can
be used to set the PreallocMode parameter of blk_truncate().

Signed-off-by: Max Reitz <mreitz@redhat.com>
---
 qemu-img.c    | 33 ++++++++++++++++++++++++++++++---
 qemu-img.texi |  7 ++++++-
 2 files changed, 36 insertions(+), 4 deletions(-)

Comments

Eric Blake May 30, 2017, 8:57 p.m. UTC | #1
On 05/26/2017 11:55 AM, Max Reitz wrote:
> Add a --preallocation command line option to qemu-img resize which can
> be used to set the PreallocMode parameter of blk_truncate().
> 
> Signed-off-by: Max Reitz <mreitz@redhat.com>
> ---
>  qemu-img.c    | 33 ++++++++++++++++++++++++++++++---
>  qemu-img.texi |  7 ++++++-
>  2 files changed, 36 insertions(+), 4 deletions(-)

> @@ -3553,8 +3566,16 @@ static int img_resize(int argc, char **argv)
>          goto out;
>      }
>  
> +    current_size = blk_getlength(blk);
> +    if (current_size < 0) {
> +        error_report("Failed to inquire current image length: %s",
> +                     strerror(-current_size));
> +        ret = -1;
> +        goto out;
> +    }
> +
>      if (relative) {
> -        total_size = blk_getlength(blk) + n * relative;
> +        total_size = current_size + n * relative;

You snuck in a bug fix here (reporting failure, rather than using a
bogus total_size, if querying the size fails).  Please mention that in
the commit message.

> @@ -541,6 +541,11 @@ After using this command to grow a disk image, you must use file system and
>  partitioning tools inside the VM to actually begin using the new space on the
>  device.
>  
> +When growing an image, the @code{--preallocation} option may be used to specify
> +how the additional image area should be allocated on the host.  See the format
> +description in the @code{NOTES} section which values are allowed.  Using this
> +option may result in more data being allocated than necessary.

Should we tone it down a bit by saying 'slightly more data'?  (We'd
rather over-estimate than fall short, but our over-estimation will
probably be < 1% off, and not something drastic like an order of
magnitude off).

With the improved commit message,
Reviewed-by: Eric Blake <eblake@redhat.com>
Stefan Hajnoczi May 31, 2017, 10:09 a.m. UTC | #2
On Fri, May 26, 2017 at 06:55:06PM +0200, Max Reitz wrote:
> Add a --preallocation command line option to qemu-img resize which can
> be used to set the PreallocMode parameter of blk_truncate().
> 
> Signed-off-by: Max Reitz <mreitz@redhat.com>
> ---
>  qemu-img.c    | 33 ++++++++++++++++++++++++++++++---
>  qemu-img.texi |  7 ++++++-
>  2 files changed, 36 insertions(+), 4 deletions(-)

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Max Reitz May 31, 2017, 12:12 p.m. UTC | #3
On 2017-05-30 22:57, Eric Blake wrote:
> On 05/26/2017 11:55 AM, Max Reitz wrote:
>> Add a --preallocation command line option to qemu-img resize which can
>> be used to set the PreallocMode parameter of blk_truncate().
>>
>> Signed-off-by: Max Reitz <mreitz@redhat.com>
>> ---
>>  qemu-img.c    | 33 ++++++++++++++++++++++++++++++---
>>  qemu-img.texi |  7 ++++++-
>>  2 files changed, 36 insertions(+), 4 deletions(-)
> 
>> @@ -3553,8 +3566,16 @@ static int img_resize(int argc, char **argv)
>>          goto out;
>>      }
>>  
>> +    current_size = blk_getlength(blk);
>> +    if (current_size < 0) {
>> +        error_report("Failed to inquire current image length: %s",
>> +                     strerror(-current_size));
>> +        ret = -1;
>> +        goto out;
>> +    }
>> +
>>      if (relative) {
>> -        total_size = blk_getlength(blk) + n * relative;
>> +        total_size = current_size + n * relative;
> 
> You snuck in a bug fix here (reporting failure, rather than using a
> bogus total_size, if querying the size fails).  Please mention that in
> the commit message.
> 
>> @@ -541,6 +541,11 @@ After using this command to grow a disk image, you must use file system and
>>  partitioning tools inside the VM to actually begin using the new space on the
>>  device.
>>  
>> +When growing an image, the @code{--preallocation} option may be used to specify
>> +how the additional image area should be allocated on the host.  See the format
>> +description in the @code{NOTES} section which values are allowed.  Using this
>> +option may result in more data being allocated than necessary.
> 
> Should we tone it down a bit by saying 'slightly more data'?  (We'd
> rather over-estimate than fall short, but our over-estimation will
> probably be < 1% off, and not something drastic like an order of
> magnitude off).

I wanted to be on the safe side for future updates for other formats
(where I'm not sure how well we can do this).

I somehow have the feeling that XFS preallocation may play its game,
too, although I can't seem to trigger it...

Anyway, as long as we can justify, say, ~10 % as "slightly", I'm OK with
adding it.

> With the improved commit message,
> Reviewed-by: Eric Blake <eblake@redhat.com>

Will do, and as always: Thanks!

Max

Patch
diff mbox

diff --git a/qemu-img.c b/qemu-img.c
index 236fd2e..7463424 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -24,6 +24,7 @@ 
 #include "qemu/osdep.h"
 #include "qemu-version.h"
 #include "qapi/error.h"
+#include "qapi/util.h"
 #include "qapi-visit.h"
 #include "qapi/qobject-output-visitor.h"
 #include "qapi/qmp/qerror.h"
@@ -62,6 +63,7 @@  enum {
     OPTION_NO_DRAIN = 262,
     OPTION_TARGET_IMAGE_OPTS = 263,
     OPTION_SIZE = 264,
+    OPTION_PREALLOCATION = 265,
 };
 
 typedef enum OutputFormat {
@@ -3435,9 +3437,10 @@  static int img_resize(int argc, char **argv)
     Error *err = NULL;
     int c, ret, relative;
     const char *filename, *fmt, *size;
-    int64_t n, total_size;
+    int64_t n, total_size, current_size;
     bool quiet = false;
     BlockBackend *blk = NULL;
+    PreallocMode prealloc = PREALLOC_MODE_OFF;
     QemuOpts *param;
 
     static QemuOptsList resize_options = {
@@ -3471,6 +3474,7 @@  static int img_resize(int argc, char **argv)
             {"help", no_argument, 0, 'h'},
             {"object", required_argument, 0, OPTION_OBJECT},
             {"image-opts", no_argument, 0, OPTION_IMAGE_OPTS},
+            {"preallocation", required_argument, 0, OPTION_PREALLOCATION},
             {0, 0, 0, 0}
         };
         c = getopt_long(argc, argv, ":f:hq",
@@ -3505,6 +3509,15 @@  static int img_resize(int argc, char **argv)
         case OPTION_IMAGE_OPTS:
             image_opts = true;
             break;
+        case OPTION_PREALLOCATION:
+            prealloc = qapi_enum_parse(PreallocMode_lookup, optarg,
+                                       PREALLOC_MODE__MAX, PREALLOC_MODE__MAX,
+                                       NULL);
+            if (prealloc == PREALLOC_MODE__MAX) {
+                error_report("Invalid preallocation mode '%s'", optarg);
+                return 1;
+            }
+            break;
         }
     }
     if (optind != argc - 1) {
@@ -3553,8 +3566,16 @@  static int img_resize(int argc, char **argv)
         goto out;
     }
 
+    current_size = blk_getlength(blk);
+    if (current_size < 0) {
+        error_report("Failed to inquire current image length: %s",
+                     strerror(-current_size));
+        ret = -1;
+        goto out;
+    }
+
     if (relative) {
-        total_size = blk_getlength(blk) + n * relative;
+        total_size = current_size + n * relative;
     } else {
         total_size = n;
     }
@@ -3564,7 +3585,13 @@  static int img_resize(int argc, char **argv)
         goto out;
     }
 
-    ret = blk_truncate(blk, total_size, PREALLOC_MODE_OFF, &err);
+    if (total_size <= current_size && prealloc != PREALLOC_MODE_OFF) {
+        error_report("Preallocation can only be used for growing images");
+        ret = -1;
+        goto out;
+    }
+
+    ret = blk_truncate(blk, total_size, prealloc, &err);
     if (!ret) {
         qprintf(quiet, "Image resized.\n");
     } else {
diff --git a/qemu-img.texi b/qemu-img.texi
index 3db035f..64bcf87 100644
--- a/qemu-img.texi
+++ b/qemu-img.texi
@@ -529,7 +529,7 @@  qemu-img rebase -b base.img diff.qcow2
 At this point, @code{modified.img} can be discarded, since
 @code{base.img + diff.qcow2} contains the same information.
 
-@item resize @var{filename} [+ | -]@var{size}
+@item resize [--preallocation=@var{prealloc}] @var{filename} [+ | -]@var{size}
 
 Change the disk image as if it had been created with @var{size}.
 
@@ -541,6 +541,11 @@  After using this command to grow a disk image, you must use file system and
 partitioning tools inside the VM to actually begin using the new space on the
 device.
 
+When growing an image, the @code{--preallocation} option may be used to specify
+how the additional image area should be allocated on the host.  See the format
+description in the @code{NOTES} section which values are allowed.  Using this
+option may result in more data being allocated than necessary.
+
 @item amend [-p] [-f @var{fmt}] [-t @var{cache}] -o @var{options} @var{filename}
 
 Amends the image format specific @var{options} for the image file