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Re: [Qemu-block] [PATCH 1/7] block: fix comment for bdrv_get_allocated_f

From: Eric Blake
Subject: Re: [Qemu-block] [PATCH 1/7] block: fix comment for bdrv_get_allocated_file_size()
Date: Thu, 25 May 2017 12:46:46 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.1.0

On 05/25/2017 12:03 PM, Vladimir Sementsov-Ogievskiy wrote:
> 25.05.2017 19:32, Eric Blake wrote:
>> On 05/25/2017 10:26 AM, Vladimir Sementsov-Ogievskiy wrote:
>>> Current comment is not clear enough: which sparseness is meant, coming
>>> from sparse image format or from sparse file system?
>>> For example, if we have qcow2 above raw file on non-sparse file system,
>>> this function will say nothing about unallocated (by qcow2 layer)
>>> clusters.

>>> + * Size of allocated in underlying file system area. Sparseness is
>>> taken into
>> Doesn't read well.  Maybe: s/Size of allocated/Allocation size/ ?
>>> + * account for sparse file systems. Return < 0 if error or unknown.
>> I still don't get what we are trying to present.

>> I think we still need to do a better job at writing a precise comment.
> bdrv_get_allocated_file_size is not related to qcow2, as qcow2 doesn't
> support it. So, it is finally just raw_get_allocated_file_size, which
> returns st.st_blocks * 512 after fstat(s->fd).
> It will correspond to qcow2 sparseness if qcow2 discarded corresponding
> clusters in bs->file and if underlying fs is sparse.

Okay, that helps.  How about this wording:

Allocation size of the underlying file system area.  Sparseness is taken
into account (holes do not contribute to this size).  Return < 0 if
error or unknown.

Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

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