Re: How to find what symlink points to?
On Monday 27 July 2009 20:54:51 Unga wrote:
> Thanks everybody for valuable replies. In fact, I also used readlink(2) but
> fed the symlink path directly from dirent, which was partial, readlink(2)
> requires full path.
Nope it doesn't. It's the classical "opendir does not chdir" problem.
readlink(2) requires a path that resolves from the current working directory
of the program. If you opendir(3) /dev and are in /, then dirent->d_name is
not valid for your cwd. Either you have to chdir or prepend the path given to
opendir to dirent->d_name.
% ./rl /dev/stdout
stdout => fd/1
See the diff on previous rl.c below.
--
Mel
--- rl.c.orig 2009-07-27 09:19:58.0 -0800
+++ rl.c2009-07-27 21:25:48.0 -0800
@@ -9,13 +9,31 @@
int main(int argc, char **argv)
{
- char path[MAXPATHLEN], buf[MAXPATHLEN+1];
+ char path[MAXPATHLEN], buf[MAXPATHLEN+1], *ptr;
ssize_t res;
if( argc != 2 )
exit(67);
(void)strlcpy(path, argv[1], sizeof(path));
+ ptr = strrchr(path, '/');
+ if( ptr != NULL )
+ {
+ char *tmp = ptr + 1;
+
+ if( ptr == path )
+ {
+ if( strlen(path) == 1 )
+ errx(67, "/ can never be a symlink");
+ chdir("/");
+ }
+ else
+ {
+ *ptr = '\0';
+ (void)chdir(path);
+ }
+ (void)strlcpy(path, tmp, sizeof(path));
+ }
res = readlink(path, buf, sizeof(buf));
if( res < 0 )
err(EXIT_FAILURE, "readlink()");
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Re: How to find what symlink points to?
--- On Tue, 7/28/09, Mel Flynn
wrote:
> From: Mel Flynn
> Subject: Re: How to find what symlink points to?
> To: freebsd-questions@freebsd.org
> Date: Tuesday, July 28, 2009, 1:25 AM
> On Monday 27 July 2009 05:45:13 Unga
> wrote:
>
> > > > Hi all
> > > >
> > > > I need to remove some unwanted symlinks on
> /dev using
> > >
> > > a C program.
> > >
> > > > The "struct dirent" only shows the symlink
> name, how
> > >
> > > do I find what that
> > >
> > > > symlink points to for verification purpose?
> > >
> > > By using the readlink(2) system call.
> >
> > But readlink(2) fails with errno set to 2. Can
> readlink(2) use with dev
> > nodes?
>
> Works for me. errno 2 is ENOENT ("No such file or
> directory"). I would inspect
> if your request path points to the right location.
>
> % ./rl /dev/stderr
> /dev/stderr => fd/2
>
> % cat rl.c
> #include
> #include
> #include
> #include
> #include
> #include
>
> #include
>
> int main(int argc, char **argv)
> {
> char path[MAXPATHLEN],
> buf[MAXPATHLEN+1];
> ssize_t res;
>
> if( argc != 2 )
>
> exit(67);
>
> (void)strlcpy(path, argv[1],
> sizeof(path));
> res = readlink(path, buf,
> sizeof(buf));
> if( res < 0 )
>
> err(EXIT_FAILURE, "readlink()");
> buf[MAXPATHLEN] = '\0';
> printf("%s => %s\n", path,
> buf);
>
> return (0);
> }
>
Thanks everybody for valuable replies. In fact, I also used readlink(2) but fed
the symlink path directly from dirent, which was partial, readlink(2) requires
full path.
Unga
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Re: How to find what symlink points to?
On Monday 27 July 2009 05:45:13 Unga wrote:
> > > Hi all
> > >
> > > I need to remove some unwanted symlinks on /dev using
> >
> > a C program.
> >
> > > The "struct dirent" only shows the symlink name, how
> >
> > do I find what that
> >
> > > symlink points to for verification purpose?
> >
> > By using the readlink(2) system call.
>
> But readlink(2) fails with errno set to 2. Can readlink(2) use with dev
> nodes?
Works for me. errno 2 is ENOENT ("No such file or directory"). I would inspect
if your request path points to the right location.
% ./rl /dev/stderr
/dev/stderr => fd/2
% cat rl.c
#include
#include
#include
#include
#include
#include
#include
int main(int argc, char **argv)
{
char path[MAXPATHLEN], buf[MAXPATHLEN+1];
ssize_t res;
if( argc != 2 )
exit(67);
(void)strlcpy(path, argv[1], sizeof(path));
res = readlink(path, buf, sizeof(buf));
if( res < 0 )
err(EXIT_FAILURE, "readlink()");
buf[MAXPATHLEN] = '\0';
printf("%s => %s\n", path, buf);
return (0);
}
--
Mel
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Re: How to find what symlink points to?
On Mon, Jul 27, 2009 at 8:45 AM, Unga wrote: > > --- On Mon, 7/27/09, Erik Trulsson wrote: > >> From: Erik Trulsson >> Subject: Re: How to find what symlink points to? >> To: "Unga" >> Cc: freebsd-questions@freebsd.org >> Date: Monday, July 27, 2009, 9:36 PM >> On Mon, Jul 27, 2009 at 05:44:59AM >> -0700, Unga wrote: >> > >> > Hi all >> > >> > I need to remove some unwanted symlinks on /dev using >> a C program. >> > >> > The "struct dirent" only shows the symlink name, how >> do I find what that >> > symlink points to for verification purpose? >> >> By using the readlink(2) system call. >> > > But readlink(2) fails with errno set to 2. Can readlink(2) use with dev nodes? > > Unga > Doesn't 'ls -alh' provide that information? Andrew ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to "freebsd-questions-unsubscr...@freebsd.org"
Re: How to find what symlink points to?
--- On Mon, 7/27/09, Erik Trulsson wrote: > From: Erik Trulsson > Subject: Re: How to find what symlink points to? > To: "Unga" > Cc: freebsd-questions@freebsd.org > Date: Monday, July 27, 2009, 9:36 PM > On Mon, Jul 27, 2009 at 05:44:59AM > -0700, Unga wrote: > > > > Hi all > > > > I need to remove some unwanted symlinks on /dev using > a C program. > > > > The "struct dirent" only shows the symlink name, how > do I find what that > > symlink points to for verification purpose? > > By using the readlink(2) system call. > But readlink(2) fails with errno set to 2. Can readlink(2) use with dev nodes? Unga ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to "freebsd-questions-unsubscr...@freebsd.org"
Re: How to find what symlink points to?
On Mon, Jul 27, 2009 at 05:44:59AM -0700, Unga wrote: > > Hi all > > I need to remove some unwanted symlinks on /dev using a C program. > > The "struct dirent" only shows the symlink name, how do I find what that > symlink points to for verification purpose? By using the readlink(2) system call. -- Erik Trulsson ertr1...@student.uu.se ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to "freebsd-questions-unsubscr...@freebsd.org"
