[uml-devel] [PATCH 0/2] Fixes for umid code for 2.6.17

[uml-devel] [PATCH 0/2] Fixes for umid code for 2.6.17

[Paolo 'Blaisorblade' Giarrusso]

Sorry, I had forgot these two ones from previous series. I've found a bug in
startup code (related to new code in 2.6.17) and here's the fix - it is not a
"just fix this", there's a tiny bit of reorganization but not much (splitting
functions and changing their return conventions).

From stg series:

+ uml-not_dead_yet-remove-existing-dir   | uml: fix not_dead_yet when
	directory is in bad state
+ uml-rename-improve-actually_do_remove  | uml: rename and improve
	actually_do_remove()

-- 
Inform me of my mistakes, so I can keep imitating Homer Simpson's "Doh!".
Paolo Giarrusso, aka Blaisorblade (Skype ID "PaoloGiarrusso", ICQ 215621894)
http://www.user-mode-linux.org/~blaisorblade


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[uml-devel] [PATCH 1/2] uml: fix not_dead_yet when directory is in bad state

[Paolo 'Blaisorblade' Giarrusso]

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);


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[uml-devel] [PATCH 2/2] uml: rename and improve actually_do_remove()

[Paolo 'Blaisorblade' Giarrusso]

From: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>

Rename actually_do_remove() to remove_files_and_dir(), make it call closedir(),
make it ignore ENOENT (I see it frequently enough).

ENOENT is probably due to multiple threads calling the exitcall functions
together*, but fixing that is non-trivial; and ignoring it is perfectly ok in
any case.

* it can surely happen: last_ditch_exit() is installed as SIGTERM handler at
boot, and it's not removed on thread creation. So killall vmlinux (which I do)
surely causes that. I've seen also a crash which seems to do the same.

Installing the handler on only the main thread would make UML do no cleanup when
another thread exits, and we're not sure we want that. And mutual exclusion in
that context is tricky - we can't use spinlock in code not on a kernel stack
(spinlock debugging uses "current" a lot).

Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
---

 arch/um/os-Linux/umid.c |   53 +++++++++++++++++++++++++++++++++--------------
 1 files changed, 37 insertions(+), 16 deletions(-)

diff --git a/arch/um/os-Linux/umid.c b/arch/um/os-Linux/umid.c
index 7c53be1..8ef150f 100644
--- a/arch/um/os-Linux/umid.c
+++ b/arch/um/os-Linux/umid.c
@@ -67,32 +67,53 @@ err:
 	return err;
 }
 
-static int actually_do_remove(char *dir)
+/*
+ * Unlinks the files contained in @dir and then removes @dir.
+ * Doesn't handle directory trees, so it's not like rm -rf, but almost such. We
+ * ignore ENOENT errors for anything (they happen, strangely enough - possibly due
+ * to races between multiple dying UML threads).
+ */
+static int remove_files_and_dir(char *dir)
 {
 	DIR *directory;
 	struct dirent *ent;
 	int len;
 	char file[256];
+	int ret;
 
 	directory = opendir(dir);
-	if(directory == NULL)
-		return -errno;
+	if (directory == NULL) {
+		if (errno != ENOENT)
+			return -errno;
+		else
+			return 0;
+	}
 
-	while((ent = readdir(directory)) != NULL){
-		if(!strcmp(ent->d_name, ".") || !strcmp(ent->d_name, ".."))
+	while ((ent = readdir(directory)) != NULL) {
+		if (!strcmp(ent->d_name, ".") || !strcmp(ent->d_name, ".."))
 			continue;
 		len = strlen(dir) + sizeof("/") + strlen(ent->d_name) + 1;
-		if(len > sizeof(file))
-			return -E2BIG;
+		if (len > sizeof(file)) {
+			ret = -E2BIG;
+			goto out;
+		}
 
 		sprintf(file, "%s/%s", dir, ent->d_name);
-		if(unlink(file) < 0)
-			return -errno;
+		if (unlink(file) < 0 && errno != ENOENT) {
+			ret = -errno;
+			goto out;
+		}
 	}
-	if(rmdir(dir) < 0)
-		return -errno;
 
-	return 0;
+	if (rmdir(dir) < 0 && errno != ENOENT) {
+		ret = -errno;
+		goto out;
+	}
+
+	ret = 0;
+out:
+	closedir(directory);
+	return ret;
 }
 
 /* This says that there isn't already a user of the specified directory even if
@@ -172,9 +193,9 @@ static int umdir_take_if_dead(char *dir)
 	if (is_umdir_used(dir))
 		return -EEXIST;
 
-	ret = actually_do_remove(dir);
+	ret = remove_files_and_dir(dir);
 	if (ret) {
-		printk("is_umdir_used - actually_do_remove failed with "
+		printk("is_umdir_used - remove_files_and_dir failed with "
 		       "err = %d\n", ret);
 	}
 	return ret;
@@ -354,9 +375,9 @@ static void remove_umid_dir(void)
 	char dir[strlen(uml_dir) + UMID_LEN + 1], err;
 
 	sprintf(dir, "%s%s", uml_dir, umid);
-	err = actually_do_remove(dir);
+	err = remove_files_and_dir(dir);
 	if(err)
-		printf("remove_umid_dir - actually_do_remove failed with "
+		printf("remove_umid_dir - remove_files_and_dir failed with "
 		       "err = %d\n", err);
 }
 


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