record: Find the execution binary in PATH

[honggyukim]

Currently uftrace explicitly requires to have a correct pathname, so it
has to be used with full pathname as follows:

$ uftrace --force /usr/bin/python -c ''

This patch allows the user can provide the command name, which is placed
one of directories in PATH environment.
So uftrace can be simply used as follows:

$ uftrace --force python -c ''

It'd be helpful especially when tracing with -P option and it will make
easier to use full dynamic tracing feature as follows:

$ uftrace -P. -a python -c 'print("Hi, Python")'

Closes: #474

Signed-off-by: Honggyu Kim [email protected]

[honggyukim]

Hi @namhyung, I think we better find the executable file in PATH environment for easier usage.

$ uftrace -P. -a echo "Hello"
Hello
# DURATION     TID     FUNCTION
 321.932 us [177318] | getenv("POSIXLY_CORRECT") = "NULL";
   1.644 us [177318] | strrchr("echo", '/') = "NULL";
  62.873 us [177318] | setlocale(LC_ALL, "") = "en_US.UTF-8";
   7.377 us [177318] | bindtextdomain("coreutils", "/usr/share/locale");
   1.876 us [177318] | textdomain("coreutils");
   1.037 us [177318] | __cxa_atexit();
   1.454 us [177318] | strcmp("Hello", "--help") = 27;
   0.523 us [177318] | strcmp("Hello", "--version") = 27;
   3.773 us [177318] | fputs_unlocked();
  12.184 us [177318] | __overflow();
   1.457 us [177318] | __fpending();
   1.280 us [177318] | fileno(&_IO_2_1_stdout_) = 1;
   0.803 us [177318] | __freading();
   0.190 us [177318] | __freading();
   1.104 us [177318] | fflush(&_IO_2_1_stdout_) = 0;
   2.580 us [177318] | fclose(&_IO_2_1_stdout_) = 0;
   0.184 us [177318] | __fpending();
   0.307 us [177318] | fileno(&_IO_2_1_stderr_) = 2;
   0.163 us [177318] | __freading();
   0.146 us [177318] | __freading();
   0.376 us [177318] | fflush(&_IO_2_1_stderr_) = 0;
   1.230 us [177318] | fclose(&_IO_2_1_stderr_) = 0;

I thought that giving a full pathname or using which command doesn't looks nice for general users.
It can be used just like any other tracing tools such as strace, ltrace, etc. Please let me know how you think about it.

[namhyung]

You'd better using strv for this kind of string handling.

[honggyukim]

Applied.

[namhyung]

What about moving this under the find_in_path()?

[honggyukim]

If I move this message inside find_in_path, then it will not print anything when the user gives the full pathname. The first is_regular_executable check will be successful so doesn't call find_in_path in this case.

[namhyung]

Oh, I meant the callsite - as find_in_path() can change the exename, it'd be nice to print the final name IMO.

[honggyukim]

I see. I think it's enough to place after the searching the binary as I updated. Thanks.

[honggyukim]

@namhyung I just updated it again based on your feedback. Thanks!

[namhyung]

LGTM

[honggyukim]

Thanks for merging this. Let's modify documents that includes the absolute path and which command. I mean let's keep it mind before making a release, not right now. :)

[namhyung]

You can file an issue for that. :)