Jim Meyering <j...@meyering.net> writes:
> Goswin von Brederlow wrote:
>> Package: coreutils
>> Version: 8.5-1
>> Severity: normal
>> File: /bin/cp
>>
>> when copying files the size of the resulting file is known (except in
>> race conditions) beforehand and should be communicated to the
>> filesystem using posix_fallocate(). This ensures there is enough space
>> for the file and more importantly allows the filesystem to place the
>> file better, idealy as on continious chunk, on the filesystem.
>>
>> Some care must be taken to ftruncate() the file to its smaller size if
>> the source file has shrunk while copying.
>>
>> If the file has grown while copying one could posix_fallocate() to the
>> new size repeadately till the full file is copied but it probably
>> wouldn't hurt to ignore that case and just copy the remainder of the
>> grown file without allocating space first.
>
> In upstream discussion, Pádraig Brady just wrote about precisely that:
>
> http://thread.gmane.org/gmane.comp.gnu.coreutils.bugs/23023/focus=23409
Good to know this isn't completly ignored.
As a side note: This also applies to dd and might be much simpler to
handle there since dd never uses sparse files. Dd should use fallocate()
at least whenever it has a "count=xxx".
MfG
Goswin
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