On Wed, Feb 13, 2019 at 5:44 AM Qu Wenruo <quwenruo.btrfs@xxxxxxx> wrote: > > > > On 2018/10/29 下午5:43, fdmanana@xxxxxxxxxx wrote: > > From: Filipe Manana <fdmanana@xxxxxxxx> > > > > Unless the '-s' option is passed to fssum, it should not detect file holes > > and have their existence influence the computed checksum for a file. This > > tool was added to test btrfs' send/receive feature, so that it checks for > > any metadata and data differences between the original filesystem and the > > filesystem that receives send streams. > > > > For a long time the test btrfs/007, which tests btrfs' send/receive with > > fsstress, fails sporadically reporting data differences between files. > > However the md5sum/sha1sum from the reported files in the original and > > new filesystems are the same. The reason why fssum fails is because even > > in normal mode it still accounts for number of holes that exist in the > > file and their respective lengths. This is done using the SEEK_DATA mode > > of lseek. The btrfs send feature does not preserve holes nor prealloc > > extents (not supported by the current protocol), so whenever a hole or > > prealloc (unwritten) extent is detected in the source filesystem, it > > issues a write command full of zeroes, which will translate to a regular > > (written) extent in the destination filesystem. This is why fssum reports > > a different checksum. A prealloc extent also counts as hole when using > > lseek. > > > > For example when passing a seed of 1540592967 to fsstress in btrfs/007, > > the test fails, as file p0/d0/f7 has a prealloc extent in the original > > filesystem (in the incr snapshot). > > > > Fix this by making fssum just read the hole file and feed its data to the > > digest calculation function when option '-s' is not given. If we ever get > > btrfs' send/receive to support holes and fallocate, we can just change > > the test and pass the '-s' option to all fssum calls. > > However this is causing more problem here. > > Now since fssum doesn't skip holes, for a super large sparse file, fssum > will try to fill all the holes with zero and spend tons of CPU time > calculating the result. Yes. So will md5sum for example and many other things. The problem is well known and it's due to the addition of the splice operation to fsstress: https://www.spinics.net/lists/fstests/msg11257.html It was also making other tests slower. This got fixed recently in the last Sunday's update by: https://www.spinics.net/lists/fstests/msg11266.html > > E.g. when seed = 1550703281. > We will have a PiB level file: > $ ls /mnt/scratch/base/p0/f3 -alh > -rw-rw-rw- 1 1441 2774 666P Feb 13 13:39 /mnt/scratch/base/p0/f3 > > (well, 666, no wonder this will fail) > > But it only takes aroud 1M: > $ du /mnt/scratch/base/p0/f3 > 1044 /mnt/scratch/base/p0/f3 > > This is even more annoying than test failure. > > Can't we just filter out the fallocate/hole punching part in the test > itself? No. Removing fallocate and hole punching operations from btrfs/007, or any other test, limits coverage. There were bugs in the past uncovered by that test exactly because fsstress exercises those operations. Further, that would not prevent creation of sparse files. Operations like pwrite, dwrite, clone, etc also cause sparse files. > > Thanks, > Qu > > > > > Signed-off-by: Filipe Manana <fdmanana@xxxxxxxx> > > --- > > src/fssum.c | 65 +++++-------------------------------------------------------- > > 1 file changed, 5 insertions(+), 60 deletions(-) > > > > diff --git a/src/fssum.c b/src/fssum.c > > index 5da39abf..f1da72fb 100644 > > --- a/src/fssum.c > > +++ b/src/fssum.c > > @@ -224,71 +224,16 @@ int > > sum_file_data_permissive(int fd, sum_t *dst) > > { > > int ret; > > - off_t pos; > > - off_t old; > > - int i; > > - uint64_t zeros = 0; > > - > > - pos = lseek(fd, 0, SEEK_CUR); > > - if (pos == (off_t)-1) > > - return errno == ENXIO ? 0 : -2; > > > > while (1) { > > - old = pos; > > - pos = lseek(fd, pos, SEEK_DATA); > > - if (pos == (off_t)-1) { > > - if (errno == ENXIO) { > > - ret = 0; > > - pos = lseek(fd, 0, SEEK_END); > > - if (pos != (off_t)-1) > > - zeros += pos - old; > > - } else { > > - ret = -2; > > - } > > - break; > > - } > > ret = read(fd, buf, sizeof(buf)); > > - assert(ret); /* eof found by lseek */ > > - if (ret <= 0) > > + if (ret < 0) > > + return -errno; > > + sum_add(dst, buf, ret); > > + if (ret < sizeof(buf)) > > break; > > - if (old < pos) /* hole */ > > - zeros += pos - old; > > - for (i = 0; i < ret; ++i) { > > - for (old = i; buf[i] == 0 && i < ret; ++i) > > - ; > > - if (old < i) /* code like a hole */ > > - zeros += i - old; > > - if (i == ret) > > - break; > > - if (zeros) { > > - if (verbose >= 2) > > - fprintf(stderr, > > - "adding %llu zeros to sum\n", > > - (unsigned long long)zeros); > > - sum_add_u64(dst, 0); > > - sum_add_u64(dst, zeros); > > - zeros = 0; > > - } > > - for (old = i; buf[i] != 0 && i < ret; ++i) > > - ; > > - if (verbose >= 2) > > - fprintf(stderr, "adding %u non-zeros to sum\n", > > - i - (int)old); > > - sum_add(dst, buf + old, i - old); > > - } > > - pos += ret; > > } > > - > > - if (zeros) { > > - if (verbose >= 2) > > - fprintf(stderr, > > - "adding %llu zeros to sum (finishing)\n", > > - (unsigned long long)zeros); > > - sum_add_u64(dst, 0); > > - sum_add_u64(dst, zeros); > > - } > > - > > - return ret; > > + return 0; > > } > > > > int > > >
