[PATCH] uml: fix not_dead_yet when directory is in bad state

The bug occurred to me when a UML left an empty ~/.uml/Sarge-norm folder -
when trying to reuse not_dead_yet() failed one of its check.  The comment
says that's ok and means that we can take the directory, but while normally
not_dead_yet() removes it and returns 0 (i.e.  go on, use this), on failure
it returns 0 but forgets to remove it.  The fix is to remove it anytime
we're going to return 0.

But since "not_dead_yet" didn't make the interface so clear, causing this
bug, and I couldn't find a convenient name for the mix of things it did, I
split it into two parts:

is_umdir_used()      -	returns a boolean, contains all checks of not_dead_yet()
umdir_take_if_dead   -	tries to remove the dir unless it's used - returns
			whether it removed it, that is we now own it.

With this changes the control flow is IMHO a bit clearer and needs less
comment for control flow.

Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Cc: Jeff Dike <jdike@addtoit.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/arch/um/os-Linux/umid.c b/arch/um/os-Linux/umid.c
index 362db059fe305d4a7276fb7c40705cb18d1a704b..d5811710126e83df198b7ff81e5cf3dabef6aa10 100644 (file)
--- a/arch/um/os-Linux/umid.c
+++ b/arch/um/os-Linux/umid.c
@@ -103,9 +103,10 @@ static int actually_do_remove(char *dir)
  *     something other than UML sticking stuff in the directory
  *     this boot racing with a shutdown of the other UML
  * In any of these cases, the directory isn't useful for anything else.
+ *
+ * Boolean return: 1 if in use, 0 otherwise.
  */
-
-static int not_dead_yet(char *dir)
+static inline int is_umdir_used(char *dir)
 {
        char file[strlen(uml_dir) + UMID_LEN + sizeof("/pid\0")];
        char pid[sizeof("nnnnn\0")], *end;
@@ -113,7 +114,7 @@ static int not_dead_yet(char *dir)
 
        n = snprintf(file, sizeof(file), "%s/pid", dir);
        if(n >= sizeof(file)){
-               printk("not_dead_yet - pid filename too long\n");
+               printk("is_umdir_used - pid filename too long\n");
                err = -E2BIG;
                goto out;
        }
@@ -123,7 +124,7 @@ static int not_dead_yet(char *dir)
        if(fd < 0) {
                fd = -errno;
                if(fd != -ENOENT){
-                       printk("not_dead_yet : couldn't open pid file '%s', "
+                       printk("is_umdir_used : couldn't open pid file '%s', "
                               "err = %d\n", file, -fd);
                }
                goto out;
@@ -132,18 +133,18 @@ static int not_dead_yet(char *dir)
        err = 0;
        n = read(fd, pid, sizeof(pid));
        if(n < 0){
-               printk("not_dead_yet : couldn't read pid file '%s', "
+               printk("is_umdir_used : couldn't read pid file '%s', "
                       "err = %d\n", file, errno);
                goto out_close;
        } else if(n == 0){
-               printk("not_dead_yet : couldn't read pid file '%s', "
+               printk("is_umdir_used : couldn't read pid file '%s', "
                       "0-byte read\n", file);
                goto out_close;
        }
 
        p = strtoul(pid, &end, 0);
        if(end == pid){
-               printk("not_dead_yet : couldn't parse pid file '%s', "
+               printk("is_umdir_used : couldn't parse pid file '%s', "
                       "errno = %d\n", file, errno);
                goto out_close;
        }
@@ -153,19 +154,32 @@ static int not_dead_yet(char *dir)
                return 1;
        }
 
-       err = actually_do_remove(dir);
-       if(err)
-               printk("not_dead_yet - actually_do_remove failed with "
-                      "err = %d\n", err);
-
-       return err;
-
 out_close:
        close(fd);
 out:
        return 0;
 }
 
+/*
+ * Try to remove the directory @dir unless it's in use.
+ * Precondition: @dir exists.
+ * Returns 0 for success, < 0 for failure in removal or if the directory is in
+ * use.
+ */
+static int umdir_take_if_dead(char *dir)
+{
+       int ret;
+       if (is_umdir_used(dir))
+               return -EEXIST;
+
+       ret = actually_do_remove(dir);
+       if (ret) {
+               printk("is_umdir_used - actually_do_remove failed with "
+                      "err = %d\n", ret);
+       }
+       return ret;
+}
+
 static void __init create_pid_file(void)
 {
        char file[strlen(uml_dir) + UMID_LEN + sizeof("/pid\0")];
@@ -244,11 +258,7 @@ int __init make_umid(void)
                if(err != -EEXIST)
                        goto err;
 
-               /* 1   -> this umid is already in use
-                * < 0 -> we couldn't remove the umid directory
-                * In either case, we can't use this umid, so return -EEXIST.
-                */
-               if(not_dead_yet(tmp) != 0)
+               if (umdir_take_if_dead(tmp) < 0)
                        goto err;
 
                err = mkdir(tmp, 0777);