generic/471: adapt test when running on btrfs to avoid failure on RWF_NOWAIT write

This test currently always fails on btrfs:

generic/471 2s ... - output mismatch (see ...results//generic/471.out.bad)
    --- tests/generic/471.out   2020-06-10 19:29:03.850519863 +0100
    +++ /home/fdmanana/git/hub/xfstests/results//generic/471.out.bad   ...
    @@ -2,12 +2,10 @@
     pwrite: Resource temporarily unavailable
     wrote 8388608/8388608 bytes at offset 0
     XXX Bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
    -RWF_NOWAIT time is within limits.
    +pwrite: Resource temporarily unavailable
    +(standard_in) 1: syntax error
    +RWF_NOWAIT took  seconds

This is because btrfs is a COW filesystem and an attempt to write into a
previously written file range allocating a new extent (or multiple).
The only exceptions are when attempting to write to a file range with a
preallocated/unwritten extent or when writing to a NOCOW file that has
extents allocated in the target range already.

The test currently expects that writing into a previously written file
range succeeds, but that is not true on btrfs since we are not dealing
with a NOCOW file. So to make the test pass on btrfs, set the NOCOW bit
on the file when the filesystem is btrfs.

Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>

diff --git a/tests/generic/471 b/tests/generic/471
index 7513f02328790e0eeeb442f6f63b4147a0b4aa3e..e9856b5201bded4b6f6f69c28a5c3ac1906fa979 100755 (executable)
--- a/tests/generic/471
+++ b/tests/generic/471
@@ -37,6 +37,17 @@ fi
 
 mkdir $testdir
 
+# Btrfs is a COW filesystem, so a RWF_NOWAIT write will always fail with -EAGAIN
+# when writing to a file range except if it's a NOCOW file and an extent for the
+# range already exists or if it's a COW file and preallocated/unwritten extent
+# exists in the target range. So to make sure that the last write succeeds on
+# all filesystems, use a NOCOW file on btrfs.
+if [ $FSTYP == "btrfs" ]; then
+       _require_chattr C
+       touch $testdir/f1
+       $CHATTR_PROG +C $testdir/f1
+fi
+
 # Create a file with pwrite nowait (will fail with EAGAIN)
 $XFS_IO_PROG -f -d -c "pwrite -N -V 1 -b 1M 0 1M" $testdir/f1