netdev - Re: [PATCH net-next] checkpatch: warn about uses of ENOTSUPP

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Date:   Sun, 10 May 2020 12:56:53 -0700
From:   Joe Perches <joe@...ches.com>
To:     Jakub Kicinski <kuba@...nel.org>, davem@...emloft.net,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     netdev@...r.kernel.org, Andrew Lunn <andrew@...n.ch>
Subject: Re: [PATCH net-next] checkpatch: warn about uses of ENOTSUPP

On Sun, 2020-05-10 at 11:51 -0700, Jakub Kicinski wrote:
> ENOTSUPP often feels like the right error code to use, but it's
> in fact not a standard Unix error. E.g.:

It is SUSv3 though.

> $ python
> > > > import errno
> > > > errno.errorcode[errno.ENOTSUPP]
> Traceback (most recent call last):
>   File "<stdin>", line 1, in <module>
> AttributeError: module 'errno' has no attribute 'ENOTSUPP'
> 
> There were numerous commits converting the uses back to EOPNOTSUPP
> but in some cases we are stuck with the high error code for backward
> compatibility reasons.
> 
> Let's try prevent more ENOTSUPPs from getting into the kernel.
> 
> Suggested-by: Andrew Lunn <andrew@...n.ch>
> Signed-off-by: Jakub Kicinski <kuba@...nel.org>
> ---
> Hi Joe, I feel like I already talked to you about this, but I lost
> my email archive, so appologies if you already said no.

Not so far as I can tell.

This seems OK to me, but using checkpatch -f should probably
not show this error.

You might include a link to where Andrew Lunn suggested it
in the commit message.  I didn't find it with a trivial search.

> diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
[]
> @@ -4199,6 +4199,14 @@ sub process {
>  			     "ENOSYS means 'invalid syscall nr' and nothing else\n" . $herecurr);
>  		}
>  
> +# ENOTSUPP is not a standard error code and should be avoided.
> +# Folks usually mean EOPNOTSUPP (also called ENOTSUP), when they type ENOTSUPP.
> +# Similarly to ENOSYS warning a small number of false positives is expected.
> +		if ($line =~ /\bENOTSUPP\b/) {

So to avoid having newbies and others trying to convert
existing uses in files using checkpatch.pl -f, maybe:
---
 scripts/checkpatch.pl | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index e5b6b9aa21d6..f1bc81d4d97c 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -4244,6 +4244,17 @@ sub process {
 			     "ENOSYS means 'invalid syscall nr' and nothing else\n" . $herecurr);
 		}
 
+# ENOTSUPP is not a standard error code and should be avoided in new patches.
+# Folks usually mean EOPNOTSUPP (also called ENOTSUP), when they type ENOTSUPP.
+# Similarly to ENOSYS warning a small number of false positives is expected.
+		if (~$file && $line =~ /\bENOTSUPP\b/) {
+			if (WARN("ENOTSUPP",
+				 "ENOTSUPP is not a SUSV4 error code, prefer EOPNOTSUPP\n" . $herecurr) &&
+			    $fix) {
+				$fixed[$fixlinenr] =~ s/\bENOTSUPP\b/EOPNOTSUPP/;
+			}
+		}
+
 # function brace can't be on same line, except for #defines of do while,
 # or if closed on same line
 		if ($perl_version_ok &&