This is needed as the basis for the readlink -f option.
Signed-off-by: Ben Hutchings <b...@decadent.org.uk>
---
v2: Don't implement the BSD/GNU extension of allowing a non-existent
last part.
Use open(O_PATH) and procfs to get resolved name from the kernel.
v3: Don't leak the fd.
--- a/usr/include/stdlib.h
+++ b/usr/include/stdlib.h
@@ -92,4 +92,6 @@ static __inline__ int grantpt(int __fd)
return 0; /* devpts does this all for us! */
}
+__extern char *realpath(const char *, char *);
+
#endif /* _STDLIB_H */
--- a/usr/klibc/Kbuild
+++ b/usr/klibc/Kbuild
@@ -60,7 +60,7 @@ klib-y += vsnprintf.o snprintf.o vsprint
send.o recv.o \
access.o chmod.o chown.o dup2.o mknod.o poll.o rename.o stat.o \
lchown.o link.o rmdir.o unlink.o utimes.o lstat.o mkdir.o \
- readlink.o select.o symlink.o pipe.o \
+ readlink.o realpath.o select.o symlink.o pipe.o \
ctype/isalnum.o ctype/isalpha.o ctype/isascii.o \
ctype/isblank.o ctype/iscntrl.o ctype/isdigit.o \
ctype/isgraph.o ctype/islower.o ctype/isprint.o \
--- /dev/null
+++ b/usr/klibc/realpath.c
@@ -0,0 +1,48 @@
+#include <fcntl.h>
+#include <limits.h>
+#include <stdlib.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+/*
+ * Note that this requires name to refer to an existing file. This is
+ * correct according to POSIX. However, BSD and GNU implementations
+ * also allow name to refer to a non-existing file in an existing
+ * directory.
+ */
+
+char *realpath(const char *name, char *resolved_name)
+{
+ static const char proc_fd_prefix[] = "/proc/self/fd/";
+ char proc_fd_name[sizeof(proc_fd_prefix) + sizeof(int) * 3];
+ int allocated = 0;
+ int fd;
+ ssize_t len;
+
+ /* Open for path lookup only */
+ fd = open(name, O_PATH);
+ if (fd < 0)
+ return NULL;
+
+ if (!resolved_name) {
+ resolved_name = malloc(PATH_MAX);
+ if (!resolved_name)
+ goto out_close;
+ allocated = 1;
+ }
+
+ /* Use procfs to read back the resolved name */
+ sprintf(proc_fd_name, "%s%d", proc_fd_prefix, fd);
+ len = readlink(proc_fd_name, resolved_name, PATH_MAX - 1);
+ if (len < 0) {
+ if (allocated)
+ free(resolved_name);
+ resolved_name = NULL;
+ } else {
+ resolved_name[len] = 0;
+ }
+
+out_close:
+ close(fd);
+ return resolved_name;
+}
--
Ben Hutchings
One of the nice things about standards is that there are so many of them.
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