Re: [Qemu-block] [PATCH] file-posix: add rough-block-status parameter

[Denis V . Lunev]

On 1/9/19 8:09 PM, Kevin Wolf wrote:
> Am 09.01.2019 um 17:55 hat Paolo Bonzini geschrieben:
>> On 09/01/19 17:51, Kevin Wolf wrote:
>>> Am 09.01.2019 um 17:42 hat Paolo Bonzini geschrieben:
>>>> On 09/01/19 12:23, Kevin Wolf wrote:
>>>>> Also note that this is only metadata preallocation; full preallocation
>>>>> will still return allocated for the protocol layer and so it will always
>>>>> be slow.
>>>> Full preallocation these days can create images with preallocated but
>>>> known-zero blocks, I think?
>>> That would defeat one of the main purposes of preallocation because it
>>> would still require COW and metadata updates on the first write.
>> Sorry I mean at the protocol level, like FALLOC_FL_ZERO_RANGE.  It would
>> still require metadata updates on the filesystem level, unlike "real"
>> full preallocation, but no qcow2 metadata updates.
> preallocation=full doesn't do that. preallocation=falloc is more like
> it, though that is just posix_fallocate(), not FALLOC_FL_ZERO_RANGE. But
> when called on a new file, it might result in the same thing? Not sure.
>
> Kevin
From the point of the file structure "fallocated" space should be considered
as data as the space on the disc is really allocated and the same constraint
should be kept in on target.

Den