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SubjectRe: [PATCH 2/2] SUNRPC: Optimize 'svc_print_xprts()'
On Thu, Mar 26 2020, Christophe JAILLET wrote:

> Le 25/03/2020 à 23:53, NeilBrown a écrit :
>> Can I suggest something more like this:
>> diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c
>> index de3c077733a7..0292f45b70f6 100644
>> --- a/net/sunrpc/svc_xprt.c
>> +++ b/net/sunrpc/svc_xprt.c
>> @@ -115,16 +115,9 @@ int svc_print_xprts(char *buf, int maxlen)
>> buf[0] = '\0';
>>
>> spin_lock(&svc_xprt_class_lock);
>> - list_for_each_entry(xcl, &svc_xprt_class_list, xcl_list) {
>> - int slen;
>> -
>> - sprintf(tmpstr, "%s %d\n", xcl->xcl_name, xcl->xcl_max_payload);
>> - slen = strlen(tmpstr);
>> - if (len + slen > maxlen)
>> - break;
>> - len += slen;
>> - strcat(buf, tmpstr);
>> - }
>> + list_for_each_entry(xcl, &svc_xprt_class_list, xcl_list)
>> + len += scnprintf(buf + len, maxlen - len, "%s %d\n",
>> + xcl->xcl_name, xcl->xcl_max_payload);
>> spin_unlock(&svc_xprt_class_lock);
>>
>> return len;
>>
>> NeilBrown
>
> Hi,
>
> this was what I suggested in the patch:
>     ---
>     This patch should have no functional change.
>     We could go further, use scnprintf and write directly in the
> destination
>     buffer. However, this could lead to a truncated last line.
>     ---

Sorry - I missed that.
So add

end = strrchr(tmpstr, '\n');
if (end)
end[1] = 0;
else
tmpstr[0] = 0;

or maybe something like
list_for_each_entry(xcl, &svc_xprt_class_list, xcl_list) {
int l = snprintf(buf + len, maxlen - len, "%s %d\n",
xcl->xcl_name, xcl->xcl_max_payload);
if (l < maxlen - len)
len += l;
}
buf[len] = 0;

There really is no need to have the secondary buffer, and I think doing
so just complicates the code.
That last version is a change of behaviour in that it will skip over
lines that are too long, rather than aborting on the first one.
I don't know which is preferred.

Thanks,
NeilBrown


>
> And Chuck Lever confirmed that:
>     That's exactly what this function is trying to avoid. As part of any
>     change in this area, it would be good to replace the current block
>     comment before this function with a Doxygen-format comment that
>     documents that goal.
>
> So, I will only send a V2 based on comments already received.
>
> CJ
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