Re: how to the filename

[Steve Graegert <graegerts@gmail.com>]

On 4/14/05, kaushal <kaushal@rocsys.com> wrote:
> Hi Steve,
>        Thanks for the response.But how will lsof work for a particular PID.If
> lsof can print all the files by their names then why can't any c
> program?The idea was to prove that the file /dev/pts/9 or some no. is
> opened by the bash and to it are the stdin,stdout and stderr
> associated.For that ,the fds 0,1,and 2 are supposed to point to the same
> file /dev/pts/9 or say /dev/tty3 ....

OK, I understand. Now I know your intention.  First of all, if you
know bash's PID you should be able to find open FDs by using the /proc
approach.  To prove that FD 0, 1 and 2 (or any FD) is associated to a
particular terminal you can use

   #include <unistd.h>
   char *ttyname(int fildes);

Hope this is what you want.

Kind Regards

    \Steve

--

Steve Graegert <graegerts@gmail.com>
Independent Software Consultant {C/C++ && Java && .NET}
Mobile: +49 (176)  21 24 88 69
Office: +49 (9131) 71 26 40 9


> This can be proved using lsof -p <PID OF THE BASH> .But how to prove
> that from within a c program?This lead to the sol if we can get the
> filename from the file descriptor and print it on the screen.
> 
> regards-
> kaushal.
> On Thu, 2005-04-14 at 16:07, Steve Graegert wrote:
> > On 4/14/05, kaushal <kaushal@rocsys.com> wrote:
> > > Hello all,
> > >        How can I get the filename/pathname given the open file descriptor?Does
> > > fstat provide this feature internally?Can somebody give the code snippet
> > > for this.
> >
> > There is no such thing.  It is not possible to obtain a FD's filename
> > reliably.  Unless you are absolutely sure that this particular FD
> > points to a file (or directory)  and not to a socket, pipe or
> > something similar, you will not be able to use fstat reliably.  Which
> > of stat's fields are suggesting to be helpful reagarding to your
> > problem?  st_ino?  How would you locate a file based on its file ID?
> > This would require scanning the complete file system (and probably
> > more than one).  Another problem is, that an FD might be associated
> > with other files at the same time or files can be stored inside a
> > directory that you can't read due to lack of sufficient permissions.
> > What you are looking for is some kind of reverse lookup to unwind the
> > many-to-one relationship of files and inodes.
> >
> > A couple of years ago Floyd Davidson suggested some code that may
> > point you to the right direction (not tested):
> >
> > /* A demo program to locate file names related to an inode number */
> >
> > #include <stdio.h>
> > #include <stdlib.h>
> > #include <unistd.h>
> > #include <string.h>
> > #include <sys/stat.h>
> > #include <dirent.h>
> > #include <limits.h>
> >
> > void scan_list(char *curdir, struct dirent **ptr_nl, int dirs);
> > int file_select(const struct dirent *nl);
> >
> > ino_t inode;
> > char curdir[PATH_MAX] = ".";    /* default search directory */
> >
> > int
> > main(int argc, char **argv)
> > {
> >   struct dirent **namelist;
> >   struct stat st;
> >
> >   if (argc < 2 || argc > 3) {
> >     fprintf(stderr,"usage:  %s inode [directory]\n", argv[0]);
> >     exit(EXIT_FAILURE);
> >   }
> >   inode = strtoul(argv[1], NULL, 10);
> >   if (!inode) {
> >     fprintf(stderr,"Error:  invalid inode\n");
> >     exit(EXIT_FAILURE);
> >   }
> >   if (argc == 3 && !lstat(argv[2], &st) && S_ISDIR(st.st_mode)) {
> >       strcpy(curdir, argv[2]);
> >   }
> >
> >   scan_list(curdir, namelist,
> >       scandir(curdir, &namelist, file_select, alphasort));
> >   return EXIT_SUCCESS;
> > }
> >
> > /*
> >  * returns 1 for directories, otherwise 0
> >  *     and displays any filename which matches inode.
> >  */
> > int
> > file_select(const struct dirent *nl)
> > {
> >   struct stat st;
> >   char curfile[PATH_MAX];
> >
> >   sprintf(curfile, "%s/%s", curdir, nl->d_name);
> >   if (0 == lstat(curfile, &st)) {
> >     /* report a matching inode number */
> >     if (st.st_ino == inode) {
> >       printf("  %6lu %-20s \n", (unsigned long) st.st_ino, curfile);
> >     }
> >     /* skip these directories */
> >     if (!strcmp(nl->d_name, ".") || !strcmp(nl->d_name, "..")) {
> >       return 0;
> >     }
> >     /* otherwise list all directories */
> >     if (S_ISDIR(st.st_mode)) {
> >       return 1;
> >     }
> >   } return 0;
> > }
> >
> > /* descend through all directories */
> > void
> > scan_list(char *olddir, struct dirent **ptr_nl, int dirs)
> > {
> >   char   savedir[PATH_MAX];
> >   int    i;
> >   struct dirent **namelist;
> >
> >   if (dirs > 0) {
> >     for (i = 0; i < dirs; ++i) {
> >       strcpy(savedir, curdir);
> >       sprintf(curdir,"%s/%s", olddir, ptr_nl[i]->d_name);
> >       scan_list(curdir, namelist,
> >          scandir(curdir, &namelist, file_select, alphasort));
> >       strcpy(curdir, savedir);
> >     }
> >   }
> > }
> >
> > /* End of demo program */
> >
> > Kind Regards
> >
> >     \Steve
> >
> > --
> >
> > Steve Graegert <graegerts@gmail.com>
> > Independent Software Consultant {C/C++ && Java && .NET}
> > Mobile: +49 (176)  21 24 88 69
> > Office: +49 (9131) 71 26 40 9
> 
>