Re: [LTP] [PATCH v1] rwtest: Confirm df is a symlink to busybox

[Petr Vorel <pvorel@suse.cz>]

> On Thu, 2023-11-30 10:41:27 +0000, Petr Vorel wrote:

> > Hi Mengchi,

> > > /bin/df can be a symlink to coreutils. It returns correct info with dir
> > > arguments.
> > > Just checking if df is a symlink will include such cases. Need to make
> > > sure it is linking to busybox before ignoring options.

> > > Signed-off-by: Mengchi Cheng <mengcc@amazon.com>
> > > ---
> > >  testcases/kernel/fs/doio/rwtest | 8 ++++----
> > >  1 file changed, 4 insertions(+), 4 deletions(-)

> > > diff --git a/testcases/kernel/fs/doio/rwtest b/testcases/kernel/fs/doio/rwtest
> > > index 6725e1426..26659e9d3 100644
> > > --- a/testcases/kernel/fs/doio/rwtest
> > > +++ b/testcases/kernel/fs/doio/rwtest
> > > @@ -329,10 +329,10 @@ do
> > >  		else
> > >  			# If df is a symlink (to busybox) then do not pass the $dir and $dfOpts
> > >  			# parameters because they don't work as expected
> > > -                        if test -h $(which df)
> > > -                           then
> > > -                               dir=""; dfOpts="";
> > > -                        fi
> > > +			if [[ "$(readlink -f "$(which df)")" == *"busybox"* ]]
> > Could you please test if this works?

> > 			if [ "$(readlink -f "$(which df)")" = "busybox" ]

> I just replaced df with a symlink cmd and the string such as zstdmt/zstd in ubuntu.
> It does not work..
> But below should work
> 			if echo "$(readlink -f "$(which df)")" | grep -q "busybox"

Yes, this would work, but this would be better:

if df --version 2>&1 | grep -q 'BusyBox'

this is way simpler and this detection is already used elsewhere.

BTW how can happen that df is symlink on coreutils?
They provide a binary, right?

> However, I linked df to /bin/busybox on my device, df -P ${dir} seems fine.
> The original code may be for a very old version of busybox.
> :/# ls -l /bin/df
> lrwxrwxrwx 1 root root 12 2023-11-16 17:49 /bin/df -> /bin/busybox
> :/# df -P tmp
> Filesystem           1024-blocks    Used Available Capacity Mounted on
> tmpfs                   280848         4    280844   0% /tmp
> :/# /usr/bin/df.coreutils -P tmp
> Filesystem     1024-blocks  Used Available Capacity Mounted on
> tmpfs               280848     4    280844       1% /tmp

> My busybox version is v1.35.0. It might be ok to remove the check completely.

-P was implemented in 2008
https://github.com/mirror/busybox/commit/d66aa3c701ffb83343239e71a8b294407ff5df86

BusyBox has often some features configurable (feature can be disabled), but if I
look correctly -P is not guarded to any config option

https://github.com/mirror/busybox/blob/master/coreutils/df.c

Therefore I'm for removing this option entirely. Please send v2.

Kind regards,
Petr

> Best,
> Mengchi

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