Thread: Issue with reading /proc/<PID>/status

More specifically getting the file size is my issue, this is what I got:

Code:

	sprintf( path, "/proc/%s/status", ent->d_name );
	file = fopen(path,"r");
	if ( !file ) {
		if ( err ) *err = errno;
		proc_glance_shut( glance );
		return NULL;
	}
	fseek( file, 0, SEEK_END );
	if ( notice->name_size < (need = ftell(file)) ) {
...
	if ( need ) {
		fseek( file, 0, SEEK_SET );
		fscanf( file, "%s", notice->name );
		fscanf( file, "%s", notice->name );
	}

I have code that reads the name after that but it always comes out as '(null)' when I pass it to printf, any ideas what I'm doing wrong?

Originally Posted by laserlight

You might want to consider parsing /proc/<PID>/stat instead as it is supposed to be more machine-readable (with say, scanf or sscanf) whereas /proc/<PID>/status is supposed to be more human-readable.

If you do want to parse /proc/<PID>/status, I don't see why you need the file size: just read line by line and parse with say, sscanf into a mapping of field name/value pairs, then extract the value corresponding to the field name that you want.

I needed the size as a work around for lack of ability to limit number of characters read into the variable without doing complicated code for fread instead, I didn't know about stat, I simply looked for a means to get the executable name via google, status is what I found in the results, I'll look into it another day, tonight I need some sleep

Originally Posted by awsdert

I needed the size as a work around for lack of ability to limit number of characters read into the variable without doing complicated code for fread instead, I didn't know about stat, I simply looked for a means to get the executable name via google, status is what I found in the results, I'll look into it another day, tonight I need some sleep

Originally Posted by Structure

I would listen...

What part of my message says I'm not listening? I needed sleep so I went to sleep, that is NOT ignoring, it is putting it off until I'm not about to drop into an unconscience state, like now

I really didn't understand what you really want.
Take a look at procfs manpage to see what /proc/[pid]/stat offer. Maybe you want something like /proc/[pid]/statm (notice the 'm' at the end).
BTW: procfs manpage will give you all entries on procfs you can use.

Originally Posted by flp1969

I really didn't understand what you really want.
Take a look at procfs manpage to see what /proc/[pid]/stat offer. Maybe you want something like /proc/[pid]/statm (notice the 'm' at the end).
BTW: procfs manpage will give you all entries on procfs you can use.

no I do not want statm, at least not yet anyways, stat or status are the only suitable ones, atm I need to get the executable name but I also need to get the parent pid later (will be using for filtering), unfortunatly both have poor design, neither declares the length of the executable name so I have to get the file size just to prevent buffer overrun when I read the name, if I can't do that then I won't be able to safely access the info further on from there either

There's also /proc/<PID>/exename if you only want the executable name:

Code:

$ cat /proc/self/exename
/usr/bin/bash

I think you'll have a problem finding the length of any file under /proc because their contents are generated on the fly by the kernel.

I would follow laserlight's advice of reading the file line by line and parsing it as you go (though with exename the contents is only the name of the executable, so there's no parsing involved). If you still want to parse /proc/<PID>/status, it's pretty easy to limit how many characters are read with scanf:

Code:

char buf[1000];
fgets(buf, sizeof buf, file);
sscanf(buf, "%100[^:]:%*[\t]%100[^\n]", key, value);

(Not tested.)

That will read a whole line and then limit the key (e.g., "Name") and value (e.g., "cat") to 100 characters each. It also properly handles spaces inside the executable name too, if the name happens to include spaces. (It assumes the key doesn't contain spaces, which is true for /proc/<PID>/status.)

(Of course, you'll need to check to see if fgets() read a complete line (if the file contains line longer than the buffer, then fgets() won't read the whole line). If the string doesn't end in a newline character, then the line in the file was too long. You'll have to decide how best to handle that situation.)

Originally Posted by flp1969

Since you want to allocate the right amount of memory to read the "executable" name, you do know scanf() can allocate the buffer dynamically, don't ya?

Code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main( void )
{
  char *buffer;

  scanf( "%ms", &buffer );

  printf( "%s (len=%zu bytes)\n", buffer, strlen( buffer ) + 1 );

  free( buffer );
}

Compiling and linking:

Code:

$ cc -O2 -o test test.c
$ ./test <<< 'ffmpeg'
ffmpeg (len=7 bytes)

true but inefficient, the app I'm working on has to go through every process looking for specific ones, having to keep allocating memory and freeing it for each process name will just slow it down hence I need to get the file size so I can just increase a shared memory as and when I need to, if I could get the length of the name before hand I would've been fine with that but alas there is no such option so file size it is

Originally Posted by christop

There's also /proc/<PID>/exename if you only want the executable name:

Code:

$ cat /proc/self/exename
/usr/bin/bash

I think you'll have a problem finding the length of any file under /proc because their contents are generated on the fly by the kernel.

I would follow laserlight's advice of reading the file line by line and parsing it as you go (though with exename the contents is only the name of the executable, so there's no parsing involved). If you still want to parse /proc/<PID>/status, it's pretty easy to limit how many characters are read with scanf:

Code:

char buf[1000];
fgets(buf, sizeof buf, file);
sscanf(buf, "%100[^:]:%*[\t]%100[^\n]", key, value);

(Not tested.)

That will read a whole line and then limit the key (e.g., "Name") and value (e.g., "cat") to 100 characters each. It also properly handles spaces inside the executable name too, if the name happens to include spaces. (It assumes the key doesn't contain spaces, which is true for /proc/<PID>/status.)

(Of course, you'll need to check to see if fgets() read a complete line (if the file contains line longer than the buffer, then fgets() won't read the whole line). If the string doesn't end in a newline character, then the line in the file was too long. You'll have to decide how best to handle that situation.)

man page never mentioned exename so I never even tried, does it provide a length at all?
as for the fgets idea I'll give it a try, probably have to put it in a loop to get the whole line but still better than a buffer overflow

Originally Posted by awsdert

man page never mentioned exename so I never even tried, does it provide a length at all?
as for the fgets idea I'll give it a try, probably have to put it in a loop to get the whole line but still better than a buffer overflow

There is no 'exename', but there is a 'comm':



Just the executable name...

Originally Posted by flp1969

There is no 'exename', but there is a 'comm':



Just the executable name...

Hehe, that's what I get for testing stuff with Cygwin instead of a real Linux system. Yep, it's "exename" in Cygwin but "comm" in Linux.