bug#6131: [PATCH]: fiemap support for efficient sparse file copy

[Jim Meyering]

Pádraig Brady wrote:
...
>> +# Require a fiemap-enabled FS.
>> +df -T -t btrfs -t xfs -t ext4 -t ocfs2 . \
>> +  || skip_ "this file system lacks FIEMAP support"
>> +
>> +# Create a large-but-sparse file.
>> +timeout 1 dd bs=1 seek=1T of=f < /dev/null || framework_failure_
>> +
>> +# Nothing can read (much less write) that many bytes in so little time.
>> +timeout 3 cp f f2 || framework_failure_
>
> I'm a bit worried with a 1s timeout.
> The following will only give false negatives over 100GB/s
>
> timeout 10 truncate -s1T f || framework_failure_
> timeout 10 cp f f2 || framework_failure_

Thanks.  Using truncate there is better, and 10 seconds is
more consistent with many other timeout-using tests.
While fixing that I noticed another problem:
the latter command should be setting fail=1.

diff --git a/tests/cp/fiemap-perf b/tests/cp/fiemap-perf
index 429e59b..6c588cb 100755
--- a/tests/cp/fiemap-perf
+++ b/tests/cp/fiemap-perf
@@ -24,9 +24,9 @@ df -T -t btrfs -t xfs -t ext4 -t ocfs2 . \
   || skip_ "this file system lacks FIEMAP support"

 # Create a large-but-sparse file.
-timeout 1 dd bs=1 seek=1T of=f < /dev/null || framework_failure_
+timeout 10 truncate -s1T f || framework_failure_

 # Nothing can read (much less write) that many bytes in so little time.
-timeout 3 cp f f2 || framework_failure_
+timeout 10 cp f f2 || fail=1

 Exit $fail


> I wouldn't worry about filling file systems either,
> as we're already limiting to ext4 etc.

Nor would I.

>> Subject: [PATCH 9/9] tests: cp/fiemap: exercise previously-failing parts
>> +# Ensure that --sparse=always can restore holes.
>> +rm -f k
>> +# Create a file starting with an "x", followed by 257K-1 0 bytes.
>> +printf x > k || framework_failure_
>> +dd bs=1k seek=1 of=k count=255 < /dev/zero || framework_failure_
>
> S/257/256/ ?

Good catch.
Initially I had count=256 and the comment was correct,
but I changed to 255 and didn't adjust.
I've corrected the comment as you suggest.

I've amended those two commits, rebased, and pushed to
a new branch: fiemap-copy-3.