find_mnt_dev.c

// Copyright (C) 2011  Pali Rohar  pali dot rohar at gmail dot com
// License: GPL

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

#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>

#include <libgen.h>

#include <mntent.h>

char * find_mnt_dir(const char * dir) {

    char save_cwd[PATH_MAX];
    char last_cwd[PATH_MAX];
    char cwd[PATH_MAX];
    char * mnt_dir = NULL;
    struct stat st;
    __dev_t last_dev;
    __ino_t last_ino;

    if ( ! getcwd(save_cwd, sizeof(save_cwd)) ) {

        fprintf(stderr, "Error: Cannot store working directory: %s\n", strerror(errno));
        return NULL;

    }

    if ( stat(dir, &st) != 0 ) {

        fprintf(stderr, "Error: Cannot stat %s: %s\n", dir, strerror(errno));
        return NULL;

    }

    if ( chdir(dir) == -1 ) {

        fprintf(stderr, "Error: Cannot change directory to %s: %s\n", dir, strerror(errno));
        return NULL;

    }

    if ( ! getcwd(last_cwd, sizeof(last_cwd)) ) {

        fprintf(stderr, "Error: Cannot get working directory: %s\n", strerror(errno));

        if ( chdir(save_cwd) == -1 )
            fprintf(stderr, "Error: Cannot restore working directory: %s\n", strerror(errno));

        return NULL;

    }

    last_dev = st.st_dev;
    last_ino = st.st_ino;

    while ( 1 ) {

        if ( chdir("..") == -1 ) {

            fprintf(stderr, "Error: Cannot change working directory: %s\n", strerror(errno));
            break;

        }

        if ( ! getcwd(cwd, sizeof(cwd)) ) {

            fprintf(stderr, "Error: Cannot get working directory: %s\n", strerror(errno));
            break;

        }

        if ( stat(cwd, &st) != 0 ) {

            fprintf(stderr, "Error: Cannot stat %s: %s\n", cwd, strerror(errno));
            break;

        }

        if ( last_dev != st.st_dev || last_ino == st.st_ino ) {

            mnt_dir = strdup(last_cwd);
            break;

        }

        if ( strcmp(cwd, "/") == 0 ) {

            mnt_dir = strdup("/");
            break;

        }

        last_dev = st.st_dev;
        last_ino = st.st_ino;
        strcpy(last_cwd, cwd);

    }

    if ( chdir(save_cwd) == -1 )
        fprintf(stderr, "Error: Cannot restore working directory: %s\n", strerror(errno));

    return mnt_dir;

}

char * find_dev(const char * mnt_dir) {

    struct mntent * mnt;
    char * dev = NULL;
    FILE * file;

    file = setmntent("/etc/mtab", "r");

    if ( ! file ) {

        fprintf(stderr, "Error: Cannot open file /etc/mtab: %s\n", strerror(errno));
        return NULL;

    }

    while ( mnt = getmntent(file) ) {

        if ( strcmp(mnt->mnt_dir, mnt_dir) == 0 ) {

            dev = strdup(mnt->mnt_fsname);
            break;

        }

    }

    endmntent(file);

    return dev;

}

int main(int argc, char * argv[]) {

    struct stat st;
    char * mnt_dir;
    char * dev;

    if ( argc != 2 ) {

        printf("Usage: %s location\n", argv[0]);
        return 1;

    }

    if ( stat(argv[1], &st) != 0 ) {

        fprintf(stderr, "Error: Cannot stat %s: %s\n", argv[1], strerror(errno));
        return 1;

    }

    if ( ! S_ISDIR(st.st_mode) )
        argv[1] = dirname(argv[1]);

    mnt_dir = find_mnt_dir(argv[1]);

    if ( ! mnt_dir ) {

        fprintf(stderr, "Error: Cannot find mount dir\n");
        return 1;

    }

    dev = find_dev(mnt_dir);

    if ( ! dev ) {

        fprintf(stderr, "Error: Cannot find device for mount dir %s\n", mnt_dir);
        free(mnt_dir);
        return 1;

    }

    printf("%s\n", dev);

    free(mnt_dir);
    free(dev);

    return 0;

}