How to tell if two files are on the same mount point?

[JanPB]

Hello. From within C++ I need to determine whether two files/directories (specified by two strings) belong to the same volume or not. How can I do that?

I tried using statfs() and statvfs() but the volume id field they return (f_fsid) is always zero for non-root users. There must be a different way to find out? I don't really need volume IDs, just a boolean value saying "same volume"/"different volumes".

Thanks!!

--
Jan

[Rubberman]

Use fstat(). You pass it a struct stat pointer that it fills out with information about the file. The structure is defined as follows (from the fstat manpage):

struct stat {
              dev_t     st_dev;     /* ID of device containing file */
              ino_t     st_ino;     /* inode number */
              mode_t    st_mode;    /* protection */
              nlink_t   st_nlink;   /* number of hard links */
              uid_t     st_uid;     /* user ID of owner */
              gid_t     st_gid;     /* group ID of owner */
              dev_t     st_rdev;    /* device ID (if special file) */
              off_t     st_size;    /* total size, in bytes */
              blksize_t st_blksize; /* blocksize for filesystem I/O */
              blkcnt_t  st_blocks;  /* number of blocks allocated */
              time_t    st_atime;   /* time of last access */
              time_t    st_mtime;   /* time of last modification */
              time_t    st_ctime;   /* time of last status change */
          };

The member you are interested in is st_dev.

FYI, this is a C language function, so it will work just fine in your code provided you #include <sys/stat.h>.

[JanPB]

The member you are interested in is st_dev.

FYI, this is a C language function, so it will work just fine in your code provided you #include <sys/stat.h>.

Thanks! I've just figured it out but it's good to know st_dev is the thing. Much appreciated.

--
Jan