Disk usage info in C/C++

Ephracis · 03-12-2006, 09:26 AM

Well, the topic says pretty much everything. It's a simple job, just get the same info as df does. But how?

kev82 · 03-12-2006, 01:21 PM

I would suggest you look into the statfs function call, make sure you check your local man pages as I think it's very non standard.

More generally, if you want to know what system calls a program makes, you can use strace.

Ephracis · 03-12-2006, 01:47 PM

Quote:

Originally Posted by kev82

I would suggest you look into the statfs function call, make sure you check your local man pages as I think it's very non standard.

I looked at the statvfs() function, is statfs() similar? Cause as far as I understand it, I can only get the size of a certain file within a filesystem that way. What I want to know is the size of the disk/partition, just like the info provided by df.

jlliagre · 03-12-2006, 02:03 PM

df doesn't give disk or partition sizes but filesystem information.

kev82 · 03-12-2006, 02:40 PM

by Ephracis
I looked at the statvfs() function, is statfs() similar?

Yes. I didn't know until now but it appears that statvfs calls statfs

by Ephracis
Cause as far as I understand it, I can only get the size of a certain file within a filesystem that way.

No, I quote from the man page for statvfs - "The function statvfs returns information about a mounted file system."

by Ephracis
What I want to know is the size of the disk/partition, just like the info provided by df.

As already stated by jlliagre, df does not return disk/partition information. It returns filesystem information. What would you expect df to say about a filesystem on a raid0 array? Information for each disk?

I quote from "strace df" to show you that it does use this system call (at least on my system)

Code:

statfs64("/home", 84, {f_type="REISERFS_SUPER_MAGIC", f_bsize=4096, f_blocks=6536975, f_bfree=1513580, f_bavail=1513580, f_files=0, f_ffree=0, f_fsid={0, 0}, f_namelen=255, f_frsize=4096}) = 0
write(1, "/dev/ida/c0d0p6       26147900  "..., 62/dev/ida/c0d0p6       26147900  20093580   6054320  77% /home
) = 62

taylor_venable · 03-13-2006, 03:05 PM

The hard, system-dependent way: pipe, fork, exec, parse.

Make a new pipe to share between two processes.
Fork; close the correct ends of the pipe.
Exec one child to "df", send output through the pipe.
Use the second child to parse the output from the first.

That's not very nice. But if you can't find the system call you want, it will work. Of course, with this method, C is hardly the ideal language...

nx5000 · 03-14-2006, 03:14 AM

Example here:
http://www.linuxquestions.org/questi...d.php?t=419927

jlliagre · 03-14-2006, 03:30 AM

And precisely your (nx5000) posting in this thread here:

http://www.linuxquestions.org/questi...37#post2126437

which shows that directly using the C apis and not popen/shell is simpler, faster and a more elegant answer to the question.

Edit: Ouch, but the sample code has a bug, the printf should be:

Code:

   printf("Bytes left:%ld\n", sbuf.f_frsize*sbuf.f_bavail);