Add readlink, xreadlink(), and change xrealloc() to not fight the stupid

compiler so much.

5 files changed, 49 insertions, 5 deletions

diff --git a/lib/lib.c b/lib/lib.c
index 6c8abb03..1f37eb59 100644
--- a/lib/lib.c
+++ b/lib/lib.c
@@ -94,10 +94,12 @@ void *xzalloc(size_t size)
 
 // Die unless we can change the size of an existing allocation, possibly
 // moving it.  (Notice different arguments from libc function.)
-void xrealloc(void **ptr, size_t size)
+void *xrealloc(void *ptr, size_t size)
 {
-	*ptr = realloc(*ptr, size);
-	if (!*ptr) error_exit("xrealloc");
+	ptr = realloc(ptr, size);
+	if (!ptr) error_exit("xrealloc");
+
+	return ptr;
 }
 
 // Die unless we can allocate a copy of this many bytes of string.
@@ -452,6 +454,30 @@ off_t fdlength(int fd)
 	return pos + 1;
 }
 
+// This can return null (meaning file not found).  It just won't return null
+// for memory allocation reasons.
+char *xreadlink(char *name)
+{
+	int len, size = 0;
+	char *buf = 0;
+
+	// Grow by 64 byte chunks until it's big enough.
+	for(;;) {
+		size +=64;
+		buf = xrealloc(buf, size);
+		len = readlink(name, buf, size);
+
+		if (len<0) {
+			free(buf);
+			return 0;
+		}
+		if (len<size) {
+			buf[len]=0;
+			return buf;
+		}
+	}
+}
+
 /*
  This might be of use or might not.  Unknown yet...
 
diff --git a/lib/lib.h b/lib/lib.h
index e2d055bc..c95a743e 100644
--- a/lib/lib.h
+++ b/lib/lib.h
@@ -40,7 +40,7 @@ void usage_exit(void);
 void strlcpy(char *dest, char *src, size_t size);
 void *xmalloc(size_t size);
 void *xzalloc(size_t size);
-void xrealloc(void **ptr, size_t size);
+void *xrealloc(void *ptr, size_t size);
 void *xstrndup(char *s, size_t n);
 void *xstrdup(char *s);
 char *xmsprintf(char *format, ...);
@@ -67,6 +67,7 @@ char *utoa(unsigned n);
 char *itoa(int n);
 long atolx(char *c);
 off_t fdlength(int fd);
+char *xreadlink(char *name);
 struct dirtree *read_dirtree_node(char *path);
 struct dirtree *read_dirtree(char *path, struct dirtree *parent);
 
diff --git a/toys/Config.in b/toys/Config.in
index 5634436c..5aae5c54 100644
--- a/toys/Config.in
+++ b/toys/Config.in
@@ -194,6 +194,22 @@ config PWD
 
 	  The print working directory command prints the current directory.
 
+config READLINK
+	bool "readlink"
+	default n
+	help
+	  usage: readlink
+
+	  Show what a symbolic link points to.
+
+config READLINK_FINAL
+	bool "readlink -f"
+	default n
+	help
+	  usage: readlink [-f]
+
+	  -f         Show final location, including normal files and multiple symlinks.
+
 config SYNC
 	bool "sync"
 	default n
diff --git a/toys/toylist.h b/toys/toylist.h
index d686877c..125b0376 100644
--- a/toys/toylist.h
+++ b/toys/toylist.h
@@ -94,6 +94,7 @@ USE_HELLO(NEWTOY(hello, NULL, TOYFLAG_USR))
 USE_MKE2FS(NEWTOY(mke2fs, MKE2FS_OPTSTRING, TOYFLAG_SBIN))
 USE_ONEIT(NEWTOY(oneit, "+<1p", TOYFLAG_SBIN))
 USE_PWD(NEWTOY(pwd, NULL, TOYFLAG_BIN))
+USE_READLINK(NEWTOY(readlink, "<1f", TOYFLAG_BIN))
 USE_TOYSH(OLDTOY(sh, toysh, "c:i", TOYFLAG_BIN))
 USE_SYNC(NEWTOY(sync, NULL, TOYFLAG_BIN))
 USE_TOUCH(NEWTOY(touch, "l#t:r:mca", TOYFLAG_BIN))
diff --git a/toys/toysh.c b/toys/toysh.c
index c383b89a..ef061bde 100644
--- a/toys/toysh.c
+++ b/toys/toysh.c
@@ -61,7 +61,7 @@ static char *parse_word(char *start, struct command **cmd)
 	// Allocate more space if there's no room for NULL terminator.
 
 	if (!((*cmd)->argc & 7))
-		xrealloc((void **)cmd,
+		*cmd=xrealloc(*cmd,
 				sizeof(struct command) + ((*cmd)->argc+8)*sizeof(char *));
 	(*cmd)->argv[(*cmd)->argc] = 0;
 	return end;