Re: [PATCH v9] scripts/bash_aliases: Add useful functions

["Alejandro Colomar (man-pages)" <alx.manpages@gmail.com>]

Hi Stefan,

On 2/27/21 4:09 PM, Stefan Puiu wrote:
> Sorry for jumping in this discussion so late, but I was wondering
> about one thing (see below).
> 
> On Fri, Feb 19, 2021 at 4:38 PM Alejandro Colomar
> <alx.manpages@gmail.com> wrote:
>> +#  grep_syscall()  finds the prototype of a syscall in the kernel sources,
>> +# printing the filename, line number, and the prototype.
>> +# It should be run from the root of the linux kernel source tree.
>> +# Usage example:  .../linux$ grep_syscall openat2;
>> +
>> +function grep_syscall()
>> +{
>> +       if ! [ -v 1 ]; then
>> +               >&2 echo "Usage: ${FUNCNAME[0]} <syscall>";
>> +               return ${EX_USAGE};
>> +       fi
>> +
>> +       find * -type f \
>> +       |grep '\.c$' \
>> +       |sort -V \
>> +       |xargs pcregrep -Mn "(?s)^\w*SYSCALL_DEFINE.\(${1},.*?\)" \
>> +       |sed -E 's/^[^:]+:[0-9]+:/&\n/';
>> +
>> +       find * -type f \
>> +       |grep '\.[ch]$' \
> 
> Any reason not to use "find . -type f -name '*.[ch]'" when you need to
> restrict the files you're looking at? I would expect that to be
> faster.

I don't like find syntax.  I never remember how all of its options work.
grep is much simpler, and everyone knows how it works.

find has: -[i]lname, -[i]name, -[i]path, -[i]regex, -[i]wholename
I don't want to be reading the manual for all of them each time I use 
find.  grep does the same with optional -i and some simple regex which 
anyone could understand with some basic regex knowledge.

For the performance part, I don't know; but we might be surprised.  At 
most it might be a bit faster (nothing like 200%), but I care more about 
readability.

I also avoid using find -exec option, and instead use xargs.  It's way 
simpler to understand, at least for me.

See also:
<http://doc.cat-v.org/unix/find-history>
<http://harmful.cat-v.org/cat-v/>

> Also, not sure what you are trying to do with 'sort -V' - why
> not feed the results directly to pcregrep?

Some consistency.  Sometimes this function finds more than one prototype 
for a syscall.  I prefer that everyone using this function gets the 
results in the same predictable order, instead of some random order.

> 
>> +       |sort -V \
>> +       |xargs pcregrep -Mn "(?s)^asmlinkage\s+[\w\s]+\**sys_${1}\s*\(.*?\)" \
>> +       |sed -E 's/^[^:]+:[0-9]+:/&\n/';
>> +}

Regards,

Alex

-- 
Alejandro Colomar
Linux man-pages comaintainer; https://www.kernel.org/doc/man-pages/
http://www.alejandro-colomar.es/