| Message ID | 20161118063943.GF27776@eguan.usersys.redhat.com (mailing list archive) |
|---|---|
| State | Superseded, archived |
| Headers | show |
On Fri, Nov 18, 2016 at 02:39:43PM +0800, Eryu Guan wrote: > On Thu, Nov 17, 2016 at 11:20:51AM -0800, Jaegeuk Kim wrote: > > This patch adds tests/generic/391 to test fsync and fdatasync with power-cuts. > > > > The rule to check is: > > 1) fsync should guarantee all the inode metadata after power-cut, > > 2) fdatasync should guarantee i_size and i_blocks at least after power-cut. > > > > Suggested-by: Chao Yu <yuchao0@huawei.com> > > Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org> > > --- > > tests/generic/391 | 136 ++++++++++++++++++++++++++++++++++++++++++++++++++ > > tests/generic/391.out | 11 ++++ > > tests/generic/group | 1 + > > 3 files changed, 148 insertions(+) > > create mode 100644 tests/generic/391 > > create mode 100644 tests/generic/391.out > > > > diff --git a/tests/generic/391 b/tests/generic/391 > > new file mode 100644 > > index 0000000..2b95151 > > --- /dev/null > > +++ b/tests/generic/391 > > @@ -0,0 +1,136 @@ > > +#! /bin/bash > > +# FS QA Test 391 > > +# > > +# Test inode's metadata after fsync or fdatasync calls. > > +# In the case of fsync, filesystem should recover all the inode metadata, while > > +# recovering i_blocks and i_size at least for fdatasync. > > +# > > +#----------------------------------------------------------------------- > > +# Copyright (c) 2016 Jaegeuk Kim. All Rights Reserved. > > +# > > +# This program is free software; you can redistribute it and/or > > +# modify it under the terms of the GNU General Public License as > > +# published by the Free Software Foundation. > > +# > > +# This program is distributed in the hope that it would be useful, > > +# but WITHOUT ANY WARRANTY; without even the implied warranty of > > +# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the > > +# GNU General Public License for more details. > > +# > > +# You should have received a copy of the GNU General Public License > > +# along with this program; if not, write the Free Software Foundation, > > +# Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA > > +#----------------------------------------------------------------------- > > +# > > + > > +seq=`basename $0` > > +seqres=$RESULT_DIR/$seq > > +echo "QA output created by $seq" > > + > > +here=`pwd` > > +tmp=/tmp/$$ > > +status=1 # failure is the default! > > +trap "_cleanup; exit \$status" 0 1 2 3 15 > > + > > +_cleanup() > > +{ > > + cd / > > + rm -f $tmp.* > > +} > > + > > +# get standard environment, filters and checks > > +. ./common/rc > > +. ./common/filter > > +. ./common/punch > > + > > +# real QA test starts here > > +_supported_fs generic > > +_supported_os Linux > > + > > +rm -f $seqres.full > > +_require_scratch > > +_require_scratch_shutdown > > +_require_xfs_io_command "fpunch" > > + > > +_scratch_mkfs >/dev/null 2>&1 > > +_scratch_mount > > + > > +testfile=$SCRATCH_MNT/testfile > > + > > +# check inode metadata after shutdown > > +check_inode_metadata() > > +{ > > + $XFS_IO_PROG -r -c "stat -v" $1 >$tmp.before > > + src/godown $SCRATCH_MNT >> $seqres.full > > + _scratch_cycle_mount > > + $XFS_IO_PROG -r -c "stat -v" $1 >$tmp.after > > + > > + if [ $FSTYP = xfs ]; then > > + sed -i '/stat.blocks/d' $tmp.before > > + sed -i '/stat.blocks/d' $tmp.after > > + fi > > Blacklist some fs "randomly" seems not easy to maintain, at least we > need some comments to explain why we do this. > > I prefer the other way Brian suggested, i.e. truncate the file to > correct size before the real fsync/fdatasync to remove any preallocated > blocks past eof. I made the following update and test passed on XFS > without problems, what do you think? I don't think that is a right way, since it breaks the existing IO behavior. I tested a little bit, and it seems the key is to call fclose to truncate out-of-eof blocks. Indeed, I could get the expected i_blocks by adding open and close after shutdown->remount; please check v3. BTW, does it make sense user needs to do fclose after power-cut to reclaim such the preallocated blocks? I feel that XFS must reclaim them during recovery on mount. Thanks, > > --- a/tests/generic/391 > +++ b/tests/generic/391 > @@ -65,10 +65,6 @@ check_inode_metadata() > _scratch_cycle_mount > $XFS_IO_PROG -r -c "stat -v" $1 >$tmp.after > > - if [ $FSTYP = xfs ]; then > - sed -i '/stat.blocks/d' $tmp.before > - sed -i '/stat.blocks/d' $tmp.after > - fi > diff $tmp.before $tmp.after >$tmp.diff > > if [ "$2" = "fdatasync" ]; then > @@ -82,13 +78,19 @@ check_inode_metadata() > } > > # append XX KB with f{data}sync, followed by power-cut > +# truncate file to the current size to avoid post-eof preallocated > +# blocks on XFS > test_i_size() > { > + local len=$2 > + local base_len=$((4 * 1024 * 1024)) > + local new_len=$((base_len + len)) > echo "==== i_size $2 test with $1 ====" | tee -a $seqres.full > - $XFS_IO_PROG -f -c "pwrite 0 4M" \ > - -c "fsync" \ > - -c "pwrite 4M $2" \ > - -c "$1" \ > + $XFS_IO_PROG -f -c "pwrite 0 $base_len" \ > + -c "fsync" \ > + -c "pwrite $base_len $len" \ > + -c "truncate $new_len" \ > + -c "$1" \ > $testfile >/dev/null > check_inode_metadata $testfile $1 > } > @@ -108,12 +110,15 @@ test_i_time() > } > > # punch XX KB with f{data}sync, followed by power-cut > +# truncate file to the current size to avoid post-eof preallocated > +# blocks on XFS > test_punch() > { > echo "==== fpunch $2 test with $1 ====" | tee -a $seqres.full > $XFS_IO_PROG -f -c "pwrite 0 4202496" \ > -c "fsync" \ > - -c "fpunch 4194304 $2"\ > + -c "fpunch 4194304 $2" \ > + -c "truncate 4202496" \ > -c "$1" \ > $testfile >/dev/null > > Thanks, > Eryu -- To unsubscribe from this list: send the line "unsubscribe linux-xfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Fri, Nov 18, 2016 at 11:44:42AM -0800, Jaegeuk Kim wrote: > On Fri, Nov 18, 2016 at 02:39:43PM +0800, Eryu Guan wrote: > > On Thu, Nov 17, 2016 at 11:20:51AM -0800, Jaegeuk Kim wrote: > > > This patch adds tests/generic/391 to test fsync and fdatasync with power-cuts. > > > > > > The rule to check is: > > > 1) fsync should guarantee all the inode metadata after power-cut, > > > 2) fdatasync should guarantee i_size and i_blocks at least after power-cut. > > > > > > Suggested-by: Chao Yu <yuchao0@huawei.com> > > > Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org> > > > --- > > > tests/generic/391 | 136 ++++++++++++++++++++++++++++++++++++++++++++++++++ > > > tests/generic/391.out | 11 ++++ > > > tests/generic/group | 1 + > > > 3 files changed, 148 insertions(+) > > > create mode 100644 tests/generic/391 > > > create mode 100644 tests/generic/391.out > > > > > > diff --git a/tests/generic/391 b/tests/generic/391 > > > new file mode 100644 > > > index 0000000..2b95151 > > > --- /dev/null > > > +++ b/tests/generic/391 > > > @@ -0,0 +1,136 @@ > > > +#! /bin/bash > > > +# FS QA Test 391 > > > +# > > > +# Test inode's metadata after fsync or fdatasync calls. > > > +# In the case of fsync, filesystem should recover all the inode metadata, while > > > +# recovering i_blocks and i_size at least for fdatasync. > > > +# > > > +#----------------------------------------------------------------------- > > > +# Copyright (c) 2016 Jaegeuk Kim. All Rights Reserved. > > > +# > > > +# This program is free software; you can redistribute it and/or > > > +# modify it under the terms of the GNU General Public License as > > > +# published by the Free Software Foundation. > > > +# > > > +# This program is distributed in the hope that it would be useful, > > > +# but WITHOUT ANY WARRANTY; without even the implied warranty of > > > +# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the > > > +# GNU General Public License for more details. > > > +# > > > +# You should have received a copy of the GNU General Public License > > > +# along with this program; if not, write the Free Software Foundation, > > > +# Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA > > > +#----------------------------------------------------------------------- > > > +# > > > + > > > +seq=`basename $0` > > > +seqres=$RESULT_DIR/$seq > > > +echo "QA output created by $seq" > > > + > > > +here=`pwd` > > > +tmp=/tmp/$$ > > > +status=1 # failure is the default! > > > +trap "_cleanup; exit \$status" 0 1 2 3 15 > > > + > > > +_cleanup() > > > +{ > > > + cd / > > > + rm -f $tmp.* > > > +} > > > + > > > +# get standard environment, filters and checks > > > +. ./common/rc > > > +. ./common/filter > > > +. ./common/punch > > > + > > > +# real QA test starts here > > > +_supported_fs generic > > > +_supported_os Linux > > > + > > > +rm -f $seqres.full > > > +_require_scratch > > > +_require_scratch_shutdown > > > +_require_xfs_io_command "fpunch" > > > + > > > +_scratch_mkfs >/dev/null 2>&1 > > > +_scratch_mount > > > + > > > +testfile=$SCRATCH_MNT/testfile > > > + > > > +# check inode metadata after shutdown > > > +check_inode_metadata() > > > +{ > > > + $XFS_IO_PROG -r -c "stat -v" $1 >$tmp.before > > > + src/godown $SCRATCH_MNT >> $seqres.full > > > + _scratch_cycle_mount > > > + $XFS_IO_PROG -r -c "stat -v" $1 >$tmp.after > > > + > > > + if [ $FSTYP = xfs ]; then > > > + sed -i '/stat.blocks/d' $tmp.before > > > + sed -i '/stat.blocks/d' $tmp.after > > > + fi > > > > Blacklist some fs "randomly" seems not easy to maintain, at least we > > need some comments to explain why we do this. > > > > I prefer the other way Brian suggested, i.e. truncate the file to > > correct size before the real fsync/fdatasync to remove any preallocated > > blocks past eof. I made the following update and test passed on XFS > > without problems, what do you think? > > I don't think that is a right way, since it breaks the existing IO behavior. > I tested a little bit, and it seems the key is to call fclose to truncate > out-of-eof blocks. Indeed, I could get the expected i_blocks by adding open and > close after shutdown->remount; please check v3. > I'm not sure what you mean by truncate breaking existing behavior. FWIW, you can probably get similar behavior by issuing the fsync in a subsequent xfs_io call rather than adding the '-c fsync' to the same xfs_io call that issues the write. This is because in most cases XFS cleans up such preallocation on file close. Do note however that if a file is repeatedly open-write-closed, the preallocation can stick around longer. > BTW, does it make sense user needs to do fclose after power-cut to reclaim such > the preallocated blocks? I feel that XFS must reclaim them during recovery on > mount. > I'm not sure there's much we can do about this, particularly since XFS uses physical style logging and thus it's not straightforward to tell when log recovery is extending the bmap of a file beyond i_size. Even then, there are cases where we can't free post-eof blocks even if we know they exist, such as when an inode has explicit (fallocate) preallocation. Brian > Thanks, > > > > > --- a/tests/generic/391 > > +++ b/tests/generic/391 > > @@ -65,10 +65,6 @@ check_inode_metadata() > > _scratch_cycle_mount > > $XFS_IO_PROG -r -c "stat -v" $1 >$tmp.after > > > > - if [ $FSTYP = xfs ]; then > > - sed -i '/stat.blocks/d' $tmp.before > > - sed -i '/stat.blocks/d' $tmp.after > > - fi > > diff $tmp.before $tmp.after >$tmp.diff > > > > if [ "$2" = "fdatasync" ]; then > > @@ -82,13 +78,19 @@ check_inode_metadata() > > } > > > > # append XX KB with f{data}sync, followed by power-cut > > +# truncate file to the current size to avoid post-eof preallocated > > +# blocks on XFS > > test_i_size() > > { > > + local len=$2 > > + local base_len=$((4 * 1024 * 1024)) > > + local new_len=$((base_len + len)) > > echo "==== i_size $2 test with $1 ====" | tee -a $seqres.full > > - $XFS_IO_PROG -f -c "pwrite 0 4M" \ > > - -c "fsync" \ > > - -c "pwrite 4M $2" \ > > - -c "$1" \ > > + $XFS_IO_PROG -f -c "pwrite 0 $base_len" \ > > + -c "fsync" \ > > + -c "pwrite $base_len $len" \ > > + -c "truncate $new_len" \ > > + -c "$1" \ > > $testfile >/dev/null > > check_inode_metadata $testfile $1 > > } > > @@ -108,12 +110,15 @@ test_i_time() > > } > > > > # punch XX KB with f{data}sync, followed by power-cut > > +# truncate file to the current size to avoid post-eof preallocated > > +# blocks on XFS > > test_punch() > > { > > echo "==== fpunch $2 test with $1 ====" | tee -a $seqres.full > > $XFS_IO_PROG -f -c "pwrite 0 4202496" \ > > -c "fsync" \ > > - -c "fpunch 4194304 $2"\ > > + -c "fpunch 4194304 $2" \ > > + -c "truncate 4202496" \ > > -c "$1" \ > > $testfile >/dev/null > > > > Thanks, > > Eryu > -- > To unsubscribe from this list: send the line "unsubscribe linux-xfs" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-xfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Fri, Nov 18, 2016 at 07:42:17PM -0500, Brian Foster wrote: > On Fri, Nov 18, 2016 at 11:44:42AM -0800, Jaegeuk Kim wrote: > > On Fri, Nov 18, 2016 at 02:39:43PM +0800, Eryu Guan wrote: > > > On Thu, Nov 17, 2016 at 11:20:51AM -0800, Jaegeuk Kim wrote: > > > > This patch adds tests/generic/391 to test fsync and fdatasync with power-cuts. > > > > > > > > The rule to check is: > > > > 1) fsync should guarantee all the inode metadata after power-cut, > > > > 2) fdatasync should guarantee i_size and i_blocks at least after power-cut. > > > > > > > > Suggested-by: Chao Yu <yuchao0@huawei.com> > > > > Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org> > > > > --- > > > > tests/generic/391 | 136 ++++++++++++++++++++++++++++++++++++++++++++++++++ > > > > tests/generic/391.out | 11 ++++ > > > > tests/generic/group | 1 + > > > > 3 files changed, 148 insertions(+) > > > > create mode 100644 tests/generic/391 > > > > create mode 100644 tests/generic/391.out > > > > > > > > diff --git a/tests/generic/391 b/tests/generic/391 > > > > new file mode 100644 > > > > index 0000000..2b95151 > > > > --- /dev/null > > > > +++ b/tests/generic/391 > > > > @@ -0,0 +1,136 @@ > > > > +#! /bin/bash > > > > +# FS QA Test 391 > > > > +# > > > > +# Test inode's metadata after fsync or fdatasync calls. > > > > +# In the case of fsync, filesystem should recover all the inode metadata, while > > > > +# recovering i_blocks and i_size at least for fdatasync. > > > > +# > > > > +#----------------------------------------------------------------------- > > > > +# Copyright (c) 2016 Jaegeuk Kim. All Rights Reserved. > > > > +# > > > > +# This program is free software; you can redistribute it and/or > > > > +# modify it under the terms of the GNU General Public License as > > > > +# published by the Free Software Foundation. > > > > +# > > > > +# This program is distributed in the hope that it would be useful, > > > > +# but WITHOUT ANY WARRANTY; without even the implied warranty of > > > > +# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the > > > > +# GNU General Public License for more details. > > > > +# > > > > +# You should have received a copy of the GNU General Public License > > > > +# along with this program; if not, write the Free Software Foundation, > > > > +# Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA > > > > +#----------------------------------------------------------------------- > > > > +# > > > > + > > > > +seq=`basename $0` > > > > +seqres=$RESULT_DIR/$seq > > > > +echo "QA output created by $seq" > > > > + > > > > +here=`pwd` > > > > +tmp=/tmp/$$ > > > > +status=1 # failure is the default! > > > > +trap "_cleanup; exit \$status" 0 1 2 3 15 > > > > + > > > > +_cleanup() > > > > +{ > > > > + cd / > > > > + rm -f $tmp.* > > > > +} > > > > + > > > > +# get standard environment, filters and checks > > > > +. ./common/rc > > > > +. ./common/filter > > > > +. ./common/punch > > > > + > > > > +# real QA test starts here > > > > +_supported_fs generic > > > > +_supported_os Linux > > > > + > > > > +rm -f $seqres.full > > > > +_require_scratch > > > > +_require_scratch_shutdown > > > > +_require_xfs_io_command "fpunch" > > > > + > > > > +_scratch_mkfs >/dev/null 2>&1 > > > > +_scratch_mount > > > > + > > > > +testfile=$SCRATCH_MNT/testfile > > > > + > > > > +# check inode metadata after shutdown > > > > +check_inode_metadata() > > > > +{ > > > > + $XFS_IO_PROG -r -c "stat -v" $1 >$tmp.before > > > > + src/godown $SCRATCH_MNT >> $seqres.full > > > > + _scratch_cycle_mount > > > > + $XFS_IO_PROG -r -c "stat -v" $1 >$tmp.after > > > > + > > > > + if [ $FSTYP = xfs ]; then > > > > + sed -i '/stat.blocks/d' $tmp.before > > > > + sed -i '/stat.blocks/d' $tmp.after > > > > + fi > > > > > > Blacklist some fs "randomly" seems not easy to maintain, at least we > > > need some comments to explain why we do this. > > > > > > I prefer the other way Brian suggested, i.e. truncate the file to > > > correct size before the real fsync/fdatasync to remove any preallocated > > > blocks past eof. I made the following update and test passed on XFS > > > without problems, what do you think? > > > > I don't think that is a right way, since it breaks the existing IO behavior. > > I tested a little bit, and it seems the key is to call fclose to truncate > > out-of-eof blocks. Indeed, I could get the expected i_blocks by adding open and > > close after shutdown->remount; please check v3. > > > > I'm not sure what you mean by truncate breaking existing behavior. FWIW, What I mean is this testcase was intended to check inode's metadata, and if we do truncate the file before fsync, I believe that would become just another testcase, when treating filesystem as a black box. > you can probably get similar behavior by issuing the fsync in a > subsequent xfs_io call rather than adding the '-c fsync' to the same > xfs_io call that issues the write. This is because in most cases XFS > cleans up such preallocation on file close. Do note however that if a > file is repeatedly open-write-closed, the preallocation can stick around > longer. Oh, right. Indeed, that is a better choice which makes sence to me. Also, I put $testfile deletion in each iteration. > > BTW, does it make sense user needs to do fclose after power-cut to reclaim such > > the preallocated blocks? I feel that XFS must reclaim them during recovery on > > mount. > > > > I'm not sure there's much we can do about this, particularly since XFS > uses physical style logging and thus it's not straightforward to tell > when log recovery is extending the bmap of a file beyond i_size. Even > then, there are cases where we can't free post-eof blocks even if we > know they exist, such as when an inode has explicit (fallocate) > preallocation. Okay, I see. Thank you for the explanation. Thanks, > > Brian > > > Thanks, > > > > > > > > --- a/tests/generic/391 > > > +++ b/tests/generic/391 > > > @@ -65,10 +65,6 @@ check_inode_metadata() > > > _scratch_cycle_mount > > > $XFS_IO_PROG -r -c "stat -v" $1 >$tmp.after > > > > > > - if [ $FSTYP = xfs ]; then > > > - sed -i '/stat.blocks/d' $tmp.before > > > - sed -i '/stat.blocks/d' $tmp.after > > > - fi > > > diff $tmp.before $tmp.after >$tmp.diff > > > > > > if [ "$2" = "fdatasync" ]; then > > > @@ -82,13 +78,19 @@ check_inode_metadata() > > > } > > > > > > # append XX KB with f{data}sync, followed by power-cut > > > +# truncate file to the current size to avoid post-eof preallocated > > > +# blocks on XFS > > > test_i_size() > > > { > > > + local len=$2 > > > + local base_len=$((4 * 1024 * 1024)) > > > + local new_len=$((base_len + len)) > > > echo "==== i_size $2 test with $1 ====" | tee -a $seqres.full > > > - $XFS_IO_PROG -f -c "pwrite 0 4M" \ > > > - -c "fsync" \ > > > - -c "pwrite 4M $2" \ > > > - -c "$1" \ > > > + $XFS_IO_PROG -f -c "pwrite 0 $base_len" \ > > > + -c "fsync" \ > > > + -c "pwrite $base_len $len" \ > > > + -c "truncate $new_len" \ > > > + -c "$1" \ > > > $testfile >/dev/null > > > check_inode_metadata $testfile $1 > > > } > > > @@ -108,12 +110,15 @@ test_i_time() > > > } > > > > > > # punch XX KB with f{data}sync, followed by power-cut > > > +# truncate file to the current size to avoid post-eof preallocated > > > +# blocks on XFS > > > test_punch() > > > { > > > echo "==== fpunch $2 test with $1 ====" | tee -a $seqres.full > > > $XFS_IO_PROG -f -c "pwrite 0 4202496" \ > > > -c "fsync" \ > > > - -c "fpunch 4194304 $2"\ > > > + -c "fpunch 4194304 $2" \ > > > + -c "truncate 4202496" \ > > > -c "$1" \ > > > $testfile >/dev/null > > > > > > Thanks, > > > Eryu > > -- > > To unsubscribe from this list: send the line "unsubscribe linux-xfs" in > > the body of a message to majordomo@vger.kernel.org > > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-xfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
--- a/tests/generic/391 +++ b/tests/generic/391 @@ -65,10 +65,6 @@ check_inode_metadata() _scratch_cycle_mount $XFS_IO_PROG -r -c "stat -v" $1 >$tmp.after - if [ $FSTYP = xfs ]; then - sed -i '/stat.blocks/d' $tmp.before - sed -i '/stat.blocks/d' $tmp.after - fi diff $tmp.before $tmp.after >$tmp.diff if [ "$2" = "fdatasync" ]; then @@ -82,13 +78,19 @@ check_inode_metadata() } # append XX KB with f{data}sync, followed by power-cut +# truncate file to the current size to avoid post-eof preallocated +# blocks on XFS test_i_size() { + local len=$2 + local base_len=$((4 * 1024 * 1024)) + local new_len=$((base_len + len)) echo "==== i_size $2 test with $1 ====" | tee -a $seqres.full - $XFS_IO_PROG -f -c "pwrite 0 4M" \ - -c "fsync" \ - -c "pwrite 4M $2" \ - -c "$1" \ + $XFS_IO_PROG -f -c "pwrite 0 $base_len" \ + -c "fsync" \ + -c "pwrite $base_len $len" \ + -c "truncate $new_len" \ + -c "$1" \ $testfile >/dev/null check_inode_metadata $testfile $1 } @@ -108,12 +110,15 @@ test_i_time() } # punch XX KB with f{data}sync, followed by power-cut +# truncate file to the current size to avoid post-eof preallocated +# blocks on XFS test_punch() { echo "==== fpunch $2 test with $1 ====" | tee -a $seqres.full $XFS_IO_PROG -f -c "pwrite 0 4202496" \ -c "fsync" \ - -c "fpunch 4194304 $2"\ + -c "fpunch 4194304 $2" \ + -c "truncate 4202496" \ -c "$1" \ $testfile >/dev/null