Re: [PATCH] copy: adjust fiemap handling of sparse files

[Jim Meyering]

Pádraig Brady wrote:
> I was looking at adding fallocate() to copy.c,
> now that the fiemap code has gone in and
> I noticed that if there was allocated space
> at the end of a file, not accounted for
> in st_size, then any holes would not be detected.

Good point.

> In what other cases does the sparse detection
> heuristic fail BTW?

There are probably a few, but none that I know of.

> Anwyay, we don't need the heuristic with fiemap,
> so I changed accordingly in the attached.
...
> Subject: [PATCH] copy: adjust fiemap handling of sparse files
>
> Don't depend on heuristics to detect sparse files
> if fiemap is available.  Also don't introduce new
> holes unless --sparse=always has been specified.

Good change, in principle.

> * src/copy.c (extent_copy): Pass the user specified
> sparse mode, and handle as described above.
> Also a redundant lseek has been suppressed when
> there is no hole between two extents.

Could that be done in two separate patches?
I haven't looked closely, but when I tested it on x86_64 (F14),
it failed like this:

    FAIL: cp/sparse-to-pipe (exit: 1)
    =================================
    ...
    + truncate -s1M sparse
    + timeout 10 cat pipe
    + cp sparse pipe
    cp: failed to extend `pipe': Invalid argument
    + fail=1
    + cmp sparse copy
    cmp: EOF on copy
    + fail=1

Sounds like the change provokes an lseek on the output FD,
even though it's a pipe.