Re: [Bug-tar] Detection of sparse files is broken on btrfs

[Joerg Schilling]

Paul Eggert <address@hidden> wrote:

> On 01/08/2018 08:54 AM, Joerg Schilling wrote:
> > The most important fact however is that allocating spade happens before you
> > copy data into that space.
>
> Certainly users need the ability to make sure there's enough room before 
> starting to copy, and POSIX allows for that with posix_fallocate. 
> However, I don't see any POSIX requirement that st_blocks has anything 
> to do with that room. For example, POSIX doesn't specify the size of the 
> units that st_blocks uses, and it even allows the unit size to vary 
> depending on the file. One cannot really deduce much of anything from 
> st_blocks, if the goal is portability to any POSIX implementation.

POSIX explains that st_blocks counts in units of DEV_BSIZE.

Jörg

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