Message-ID: <87r0788lij.fsf@gmail.com>
Date: Mon, 18 Nov 2024 23:36:12 +0530
From: Ritesh Harjani (IBM) <ritesh.list@...il.com>
To: "Darrick J. Wong" <djwong@...nel.org>
Cc: Nirjhar Roy <nirjhar@...ux.ibm.com>, fstests@...r.kernel.org, linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org, ojaswin@...ux.ibm.com, zlang@...nel.org
Subject: Re: [PATCH v2 1/2] common/rc,xfs/207: Adding a common helper function to check xflag bits on a given file

"Darrick J. Wong" <djwong@...nel.org> writes:

> On Sat, Nov 16, 2024 at 12:36:26AM +0530, Ritesh Harjani wrote:
>> "Darrick J. Wong" <djwong@...nel.org> writes:
>> 
>> > On Fri, Nov 15, 2024 at 09:45:58AM +0530, Nirjhar Roy wrote:
>> >> This patch defines a common helper function to test whether any of
>> >> fsxattr xflags field is set or not. We will use this helper in the next
>> >> patch for checking extsize (e) flag.
>> >> 
>> >> Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@...il.com>
>> >> Reviewed-by: Ojaswin Mujoo <ojaswin@...ux.ibm.com>
>> >> Signed-off-by: Nirjhar Roy <nirjhar@...ux.ibm.com>
>> >> ---
>> >>  common/rc     |  7 +++++++
>> >>  tests/xfs/207 | 13 ++-----------
>> >>  2 files changed, 9 insertions(+), 11 deletions(-)
>> >> 
>> >> diff --git a/common/rc b/common/rc
>> >> index 2af26f23..fc18fc94 100644
>> >> --- a/common/rc
>> >> +++ b/common/rc
>> >> @@ -41,6 +41,13 @@ _md5_checksum()
>> >>  	md5sum $1 | cut -d ' ' -f1
>> >>  }
>> >>  
>> >> +# Check whether a fsxattr xflags character ($2) field is set on a given file ($1).
>> >> +# e.g, fsxattr.xflags =  0x80000800 [----------e-----X]
>> >> +_test_fsx_xflags_field()
>> >
>> > How about we call this "_test_fsxattr_xflag" instead?
>> >
>> > fsx is already something else in fstests.
>> >
>> >> +{
>> >> +    grep -q "fsxattr.xflags.*\[.*$2.*\]" <($XFS_IO_PROG -c "stat" "$1")
>> >> +}
>> >
>> > Not sure why this lost the xfs_io | grep -q structure.  The return value
>> > of the whole expression will always be the return value of the last
>> > command in the pipeline.
>> >
>> 
>> I guess it was suggested here [1]
>> 
>> [1]: https://lore.kernel.org/all/20241025025651.okneano7d324nl4e@dell-per750-06-vm-08.rhts.eng.pek2.redhat.com/
>
> Ah.
>
>> root-> grep -q "hello" <(echo "hello world"); echo $?
>> 0
>> 
>> The cmd is not using the unnamed pipes ("|") any more. It's spawning the
>> process () which does echo "hello world" and creating a named pipe or
>> say temporary FD <() which is being read by grep now. So we still will
>> have the correct return value. Slightly inefficitent compared to unnamed
>> pipes though I agree. 
>
> Well... it's subtle, being bash, right? :)
>
> bash creates a pipe and a subprocess for the "echo hello world", then
> hooks its stdout to the pipe, just like a regular "|" pipe.
>
> But for "grep -q hello" things are different -- for the grep process,
> the pipe is added as a new fd (e.g. /dev/fd/63), and then that path is
> provided on the command line.  So what bash is doing is:
>
> 	grep -q "hello" /dev/fd/63
>
> AFAICT for grep this makes no difference unless you want it to tell you
> filenames:
>
> $ grep -l hello <(echo hello world)
> /dev/fd/63

aah yes, I see (from strace)

pipe2([3, 4], 0)                        = 0
fcntl(63, F_GETFD)                      = 0
fcntl(62, F_GETFD)                      = -1 EBADF (Bad file descriptor)
dup2(3, 62)                             = 62
close(3)                                = 0

Thanks!

-ritesh

> $ echo hello world | grep -l hello
> (standard input)
>
> and I'm sure there's other weird implications that I'm not remembering.
>
>> > (Correct?  I hate bash...)
>> >
>> 
>> root-> ls -la <(echo "hello world");
>> lr-x------ 1 root root 64 Nov 16 00:42 /dev/fd/63 -> 'pipe:[74211850]'
>> 
>> Did I make you hate it more? ;) 
>
> Yep!
>
> --D
>
>> 
>> -ritesh
>> 
>> > --D
>> >
>> >> +
>> >>  # Write a byte into a range of a file
>> >>  _pwrite_byte() {
>> >>  	local pattern="$1"
>> >> diff --git a/tests/xfs/207 b/tests/xfs/207
>> >> index bbe21307..4f6826f3 100755
>> >> --- a/tests/xfs/207
>> >> +++ b/tests/xfs/207
>> >> @@ -21,15 +21,6 @@ _require_cp_reflink
>> >>  _require_xfs_io_command "fiemap"
>> >>  _require_xfs_io_command "cowextsize"
>> >>  
>> >> -# Takes the fsxattr.xflags line,
>> >> -# i.e. fsxattr.xflags = 0x0 [--------------C-]
>> >> -# and tests whether a flag character is set
>> >> -test_xflag()
>> >> -{
>> >> -    local flg=$1
>> >> -    grep -q "\[.*${flg}.*\]" && echo "$flg flag set" || echo "$flg flag unset"
>> >> -}
>> >> -
>> >>  echo "Format and mount"
>> >>  _scratch_mkfs > $seqres.full 2>&1
>> >>  _scratch_mount >> $seqres.full 2>&1
>> >> @@ -65,14 +56,14 @@ echo "Set cowextsize and check flag"
>> >>  $XFS_IO_PROG -c "cowextsize 1048576" $testdir/file3 | _filter_scratch
>> >>  _scratch_cycle_mount
>> >>  
>> >> -$XFS_IO_PROG -c "stat" $testdir/file3 | grep 'fsxattr.xflags' | test_xflag "C"
>> >> +_test_fsx_xflags_field "$testdir/file3" "C" && echo "C flag set" || echo "C flag unset"
>> >>  $XFS_IO_PROG -c "cowextsize" $testdir/file3 | _filter_scratch
>> >>  
>> >>  echo "Unset cowextsize and check flag"
>> >>  $XFS_IO_PROG -c "cowextsize 0" $testdir/file3 | _filter_scratch
>> >>  _scratch_cycle_mount
>> >>  
>> >> -$XFS_IO_PROG -c "stat" $testdir/file3 | grep 'fsxattr.xflags' | test_xflag "C"
>> >> +_test_fsx_xflags_field "$testdir/file3" "C" && echo "C flag set" || echo "C flag unset"
>> >>  $XFS_IO_PROG -c "cowextsize" $testdir/file3 | _filter_scratch
>> >>  
>> >>  status=0
>> >> -- 
>> >> 2.43.5
>> >> 
>> >> 
>> 

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