xfs
[Top] [All Lists]

Re: [PATCH 1/2 v2][xfstests] Add test 257: Check proper FITRIM argument

To: Alex Elder <aelder@xxxxxxx>
Subject: Re: [PATCH 1/2 v2][xfstests] Add test 257: Check proper FITRIM argument handling
From: Lukas Czerner <lczerner@xxxxxxxxxx>
Date: Fri, 23 Sep 2011 09:38:24 +0200 (CEST)
Cc: Lukas Czerner <lczerner@xxxxxxxxxx>, xfs@xxxxxxxxxxx
In-reply-to: <1316724766.2009.78.camel@doink>
References: <1315410523-23925-1-git-send-email-lczerner@xxxxxxxxxx> <1316724766.2009.78.camel@doink>
User-agent: Alpine 2.00 (LFD 1167 2008-08-23)
On Thu, 22 Sep 2011, Alex Elder wrote:

> On Wed, 2011-09-07 at 17:48 +0200, Lukas Czerner wrote:
> > This test suppose to validate that file systems are using the fitrim
> > arguments right. It checks that the fstrim returns EINVAl in case that
> > the start of the range is beyond the end of the file system, and also
> > that the fstrim works without an error if the length of the range is
> > bigger than the file system (it should be truncated to the file system
> > length automatically within the fitrim implementation).
> > 
> > This test should also catch common problem with overflow of start+len.
> > Some file systems (ext4,xfs) had overflow problems in the past so there
> > is a specific test for it (for ext4 and xfs) as well as generic test for
> > other file systems, but it would be nice if other fs can add their
> > specific checks if this problem does apply to them as well.
> > 
> > Signed-off-by: Lukas Czerner <lczerner@xxxxxxxxxx>
> 
> I point out the same thing I did earlier on a different
> test script.  This assumes bash is able to handle >32
> bit values in its arithmetic expressions (within $(( ))).
> That could be legitimate, I just haven't found an
> authoritative answer on it.
> 
> I do know that bc supports arbitrary precision,
> so if necessary it could be used to do whatever
> calculations might exceed 32 bits.  E.g.:
> 
> function mult64() {
>         [ $# = 2 ]      || exit 1       # Not enough arguments
>         echo "$1" '*' "$2" | bc
> }

Sounds good, I think that it would be worth to have a generic helper for
doing 'bc' math.

> 
>      ...
>       agsize=65536
>       bsize=4096
>       agbytes=$(mult64 $agsize $bsize)
>       start=$(mult64 $base $agbytes)
> 
> I also have some other questions and comments
> below.  Sorry I didn't comment on your earlier
> edition.

No problem.

> 
>                                       -Alex
> 
> > ---
> > v2: add check for fsblock to agno overflow
> > 
> >  257     |  183 
> > +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> >  257.out |   14 +++++
> >  group   |    1 +
> >  3 files changed, 198 insertions(+), 0 deletions(-)
> >  create mode 100755 257
> >  create mode 100644 257.out
> > 
> > diff --git a/257 b/257
> > new file mode 100755
> > index 0000000..53efa92
> > --- /dev/null
> > +++ b/257
> > @@ -0,0 +1,183 @@
> 
> . . .
> 
> > +                   start="1152921504875282432"
> > +                   len="1152921504875282432"
> > +                   ;;
> > +   esac
> > +
> > +   _scratch_unmount
> > +   _scratch_mkfs >/dev/null 2>&1
> > +   _scratch_mount
> > +   $here/src/fstrim -s$start -l$(($fsize/2)) $SCRATCH_MNT &> /dev/null
> > +   [ $? -eq 0 ] && status=1 && echo "It seems that fs logic handling 
> > start"\
> > +                                    "argument overflows"
> 
> Please put the status assignment and echo within a proper
> if/then/fi block.  I also don't really get what's going
> on here. $? equal to 0 means success--so if it's
> successful you report "it seems that...overflows"?
> If it is right, please add a comment to make sure it's
> clear what you're doing.

Ok, I'll use proper 'if' block.

Also, the reason why fstrim should fail is because the start is clearly
beyond the end of the file system. But if the logic in FITRIM
implementation fails (as it fails in current xfs and ext4), start will
overflow and the fstrim call will succeed.

> 
> > +
> > +   _scratch_unmount
> > +   _scratch_mkfs >/dev/null 2>&1
> > +   _scratch_mount
> > +
> > +   # len should be big enough to cover the whole file system, however this
> > +   # test suppose for the overflow, so if the number of discarded bytes is
> > +   # smaller than fsize/2 than it most likely does overflow.
> > +   out=$($here/src/fstrim -v -l$len $SCRATCH_MNT)
> > +   bytes=${out%% *}
> > +
> > +   # Btrfs is special and this test does not apply to it
> 
> Do all the other tests apply though?  Why doesn't this test
> apply to btrfs as well?

All other tests are ok for btrfs. This test is checking if the logic
handling len argument is sane. fstrim is trying to discard the whole file
system, so the result (number of discarded bytes) should definitely be
almost as big as the file system (it depends on how much space is used
for metadata). Just to be sure we are checking if the discarded bytes
are at least bigger than the half of fs size. If it is smaller, there is
a problem.

The reason why btrfs is special is that it does not have all the disk space
mapped in the root tree right after the mkfs. I guess that the mapping
appears as we are trying to use more blocks. So right after mkfs, when
we are doing fstrim (which is walking the tree of free extents) there is
not enough mapped space to be trimmed and the check below would always fail.

I'll try to write a better comment.

> 
> > +   if [ $bytes -le $(($fsize*512)) ] && [ $FSTYP != "btrfs" ]; then
> > +           status=1
> > +           echo "It seems that fs logic handling len argument overflows"
> > +   fi
> > +   export MKFS_OPTIONS=$backup_mkfs_options
> > +}
> > +
> > +
> > +# get standard environment, filters and checks
> > +. ./common.rc
> > +. ./common.filter
> > +
> > +# real QA test starts here
> > +_supported_fs generic
> > +_supported_os Linux
> > +_require_scratch
> > +_scratch_mkfs >/dev/null 2>&1
> > +_scratch_mount
> > +
> > +
> > +$here/src/fstrim -l 10M $SCRATCH_MNT &> /dev/null || _notrun "FSTRIM is 
> > not supported"
> 
> You could define
>     FSTRIM="${here}/src/fstrim"
> since you use it so many times.
> 
> > +
> > +fsize=$(df -k | grep "$SCRATCH_MNT" | grep "$SCRATCH_DEV"  | awk '{print 
> > $2}')
> 
> "fssize" would be a better name.

Sure.

> 
> > +# All these tests should return EINVAL
> > +# since the start is beyond the end of
> > +# the file system
> 
> . . .
> 
> > +_scratch_unmount
> > +_scratch_mkfs >/dev/null 2>&1
> > +_scratch_mount
> > +
> > +# This is a bit fuzzy, but since the file system is fresh
> > +# there should be at least (fsize/2) free space to trim.
> > +# This is supposed to catch wrong range.len handling and overflows.
> 
> I don't really don't understand what "wrong range.len
> handling and overflows" means.

This is related to the internal FSTRIM implementation.

> 
> > +out=$($here/src/fstrim -v -s10M $SCRATCH_MNT)
> > +bytes=${out%% *}
> > +
> > +if [ $bytes -gt $(($fsize*1024)) ]; then
> > +   status=1
> > +   echo "After the full fs discard $bytes bytes were discarded"\
> > +        "however the file system is $(($fsize*1024)) bytes long."\
> > +        "This is suspicious."
> 
> Is it possible to do a meaningful test of this case
> that is reliable?  I.e., one that (almost) always
> passes so we don't have to be overly concerned about
> "suspicious" (rather than pass/fail) test results?

It is probably a badly worded. It should rather say "something is
wrong". The test is reliable and it the condition is met, then it always
means that the problem is real.

> 
> > +fi
> > +
> > +# Btrfs is special and this test does not apply to it
> > +if [ $bytes -le $(($fsize*512)) ] && [ $FSTYP != "btrfs" ]; then
> > +   status=1
> > +   echo "After the full fs discard $bytes bytes were discarded"\
> > +        "however the file system is $(($fsize*1024)) bytes long."\
> > +        "This is suspicious."
> > +fi
> > +
> > +# Now to catch overflows due to fsblk->allocation group number conversion
> > +# This is different for every file system and it also apply just to some of
> > +# them. In order to add check specific for file system you're interested in
> > +# compute the arguments as you need and make the file system with proper
> > +# alignment in function _check_conversion_overflow()
> > +_check_conversion_overflow
> 
> This is just a bit structurally odd.  That is, it seems like
> you should call a function to encapsulate setting up the
> filesystem for the tests, then just run the tests here
> (at the same "scope" as the fstrim tests run just above).

Ok, makes sense to me.

> 
> > +echo "Test done"
> > +exit
> > diff --git a/257.out b/257.out
> > new file mode 100644
> 
> . . .

Thanks!
-Lukas

<Prev in Thread] Current Thread [Next in Thread>