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 <mre...@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 <ebl...@redhat.com> Will do, and as always: Thanks! Max
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