lkml.org 
[lkml]   [2006]   [Apr]   [30]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH 1/2] uml: fix not_dead_yet when directory is in bad state
Date
From: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>

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>
---
arch/um/os-Linux/umid.c | 48 ++++++++++++++++++++++++++++-------------------
1 files changed, 29 insertions(+), 19 deletions(-)
diff --git a/arch/um/os-Linux/umid.c b/arch/um/os-Linux/umid.c
index 34bfc1b..7c53be1 100644
--- 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);
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
\
 
 \ /
  Last update: 2006-04-30 18:53    [from the cache]
©2003-2011 Jasper Spaans