Discovering hard link paths

rozeboom · 12-16-2003, 03:31 PM

How would you go about discovering the paths of a given file's hardlinks? I know you can do a stat on the file to get the link-count, but how do you find the actual paths? I want to be able to find these in a C program.

Tarts · 12-16-2003, 06:20 PM

Use 'readlink()':

Code:

#include <stdio.h>
#include <unistd.h>

int main(int *argc, char *argv[])
{
        char buf[100];
        int i = 0;
        if (!argv[1]) {
                printf("Usage: enter the path to the symlink.\n");
                return -1;
        }
        if (readlink(argv[1], buf, sizeof(buf)) == -1) {
                printf("readlink\n");
                return -1;
        }
        while (buf[i] != '\n')
                i++;
        buf[i] = '\0';
        printf("%s\n", buf);
        return 0;
}

There may be easier ways to do this.

Tarts

{edit}

'man ln', hardlinks dont have paths, mabey you mean symlink?

Tarts

kev82 · 12-18-2003, 09:09 AM

i dont think that information is stored in the filesystem because its not something you would really ever need to know. hard links must exist on the same filesystem so the only way that comes to mind is to stat every file on the filesystem and if the inode matches then youve got a link. we might be lucky enough to have a filesytem expert among us who has a better technique but thats all i can think of.

rozeboom · 12-18-2003, 09:49 AM

Thanks, Tarts, for the reply about readlink. I had found that and it appears to only give information on symlinks. The case that I am working on is for a backup application which needs to duplicate a subset of the file system. In order to produce a proper duplicate, I need to be able to determine what files are hardlinks, which I can do from stat, and then also determine how to reconstruct the same relationship on the backup disk.

Perhaps, as kev82 suggested, I may have to keep track of hardlink inodes as I step through the subset. Sounds like a workable solution, thanks!

kev82 · 12-18-2003, 10:08 AM

i suggest you have a look at the source of tar to see whats done their as the backup maybe approached in a different way.