Re: how to the filename

[Steve Graegert <graegerts@gmail.com>]

On 4/15/05, Ron Michael Khu <ronkhu@ntsp.nec.co.jp> wrote:
> Hmm..
> Im not familiar with the implementation of lsof... but I do know that
> with pstat_getproc-related functions like pstat_getfile2(),
> it is possible to retrieve information on all the open files of a
> certain process(given it's PID).  It is even possible to
> retrieve information about how many threads a particular process has
> created.

The problem I see is, that we all seem to have different thoughts
about the application of such szenarios.  Why should one try to obtain
a filename associated with an FD she did not create herself (assuming
user space applications)?  Another question is: how can one find such
FDs, or to be more specific, how can one find an FD that may be of
interest without knowing the PID (assuming that he is interested in
the FDs of a particular process).  I know it is possible (with little
effort under Linux at least) but there is no easy reverse mapping of
PIDs to their executables.  There are good reasons not to be able to
tweak FDs of other processes that easily.

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


> And like Mr. Ozgur(altunyurt@itu.edu.tr), I dont know how to retrieve
> the filename given only a filedescriptor...
> because with pstat_getfile2() Im passing PID's.
> 
> -Ron
> 
> 
> ,kaushal 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 ....
> >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
> >>
> >>
> >
> >-
> >To unsubscribe from this list: send the line "unsubscribe linux-c-programming" in
> >the body of a message to majordomo@vger.kernel.org
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> >
> >
> >
> >
> 
> 
> #include <sys/param.h>
> #include <sys/pstat.h>
> #include <sys/unistd.h>
> #include <stdio.h>
> 
> int main( int argc, char *argv[] )
> {
>    #define BURST ((size_t)10)
>    struct pst_fileinfo2 psf[BURST];
>    int i, count;
>    int idx = 0; /* index within the context */
> 
>    if ( argc != 2 )
>    {
>        printf( "args: <pid>\n" );
>        exit( 1 );
>    }
>    pid_t target = atoi( argv[1] );
> 
>    (void)printf("Open files for process PID %d\n", target);
> 
>    /* loop until all fetched */
>    while ((count = pstat_getfile2(psf, sizeof(struct pst_fileinfo2),
>                                  BURST, idx, target)) > 0) {
>             /* process them (max of BURST) at a time */
>             for (i = 0; i < count; i++) {
>                  (void)printf("fd #%d\tFSid %x:%x\tfileid %d\n",
>                         psf[i].psf_fd,
>                         psf[i].psf_id.psf_fsid.psfs_id,
>                         psf[i].psf_id.psf_fsid.psfs_type,
>                         psf[i].psf_id.psf_fileid);
>             }
> 
>             /*
>             * Now go back and do it again, using the
>              * next index after the current 'burst'
>              */
>              idx = psf[count-1].psf_fd + 1;
>    }
>    if (count == -1)
>             perror("pstat_getfile2()");
> 
>    #undef BURST
> }
> 
> 
>