minimal realpath implementation using /proc

clean and simple, but fails when the caller does not have permissions
to open the file for reading or when /proc is not available. i may
replace this with a full implementation later, possibly leaving this
version as an optimization to use when it works.

diff --git a/src/misc/realpath.c b/src/misc/realpath.c
index f6b55495781b4dbefaba09b4d33393ac476e0688..8dcf5ec9fc8792e0299b656fee5a11700ad2348a 100644 (file)
--- a/src/misc/realpath.c
+++ b/src/misc/realpath.c
@@ -1,6 +1,49 @@
 #include <stdlib.h>
+#include <stdio.h>
+#include <limits.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <errno.h>
+#include <unistd.h>
 
 char *realpath(const char *filename, char *resolved)
 {
+       int fd;
+       ssize_t r;
+       struct stat st1, st2;
+       char buf[15+3*sizeof(int)];
+       int alloc = 0;
+
+       if (!filename) {
+               errno = EINVAL;
+               return 0;
+       }
+
+       if (!resolved) {
+               alloc = 1;
+               resolved = malloc(PATH_MAX);
+               if (!resolved) return 0;
+       }
+
+       fd = open(filename, O_RDONLY|O_NONBLOCK);
+       if (fd < 0) return 0;
+       snprintf(buf, sizeof buf, "/proc/self/fd/%d", fd);
+
+       r = readlink(buf, resolved, PATH_MAX-1);
+       if (r < 0) goto err;
+       resolved[r] = 0;
+
+       fstat(fd, &st1);
+       r = stat(resolved, &st2);
+       if (r<0 || st1.st_dev != st2.st_dev || st1.st_ino != st2.st_ino) {
+               if (!r) errno = ELOOP;
+               goto err;
+       }
+
+       close(fd);
+       return resolved;
+err:
+       if (alloc) free(resolved);
+       close(fd);
        return 0;
 }