src/lib9: support renaming files

This is the standard plan 9 API for renaming files within
a directory.

Change-Id: Iae17af4b201220c7690e73bda88409fd041e7ff5

src/lib9/dirwstat.c

@@ -1,6 +1,7 @@
 #include <u.h>
 #define NOPLAN9DEFINES
 #include <libc.h>
+#include <stdio.h>
 #include <sys/time.h>
 #include <utime.h>
 #include <sys/stat.h>
@@ -9,9 +10,10 @@ int
 dirwstat(char *file, Dir *dir)
 {
 	int ret;
+	char *newfile, *p;
 	struct utimbuf ub;
 
-	/* BUG handle more */
+	/* BUG handle more (e.g. uid, gid, atime) */
 	ret = 0;
 	if(~dir->mode != 0){
 		if(chmod(file, dir->mode) < 0)
@@ -27,5 +29,20 @@ dirwstat(char *file, Dir *dir)
 		if(truncate(file, dir->length) < 0)
 			ret = -1;
 	}
+	// Note: rename after all other operations so we can use
+	// the original name in all other calls.
+	if(dir->name != nil && dir->name[0] != '\0'){
+		newfile = nil;
+		if((p = strrchr(file, '/')) != nil){
+			newfile = malloc((p-file) + 1 + strlen(dir->name) + 1);
+			if(newfile == nil)
+				return -1;
+			memmove(newfile, file, p-file+1);
+			strcpy(newfile+(p-file+1), dir->name);
+		}
+		if(rename(file, newfile != nil ? newfile : dir->name) < 0)
+			ret = -1;
+		free(newfile);
+	}
 	return ret;
 }