How to query mount propagation state?

How to query mount propagation state?

[Miklos Szeredi]

Currently one of the difficulties with mount propagations is that
there's no way to know the current state of the propagation tree.

Has anyone thought about how this info could be queried from
userspace?

Thanks,
Miklos

Re: How to query mount propagation state?

[Ram Pai]

[-- Attachment #1: Type: text/plain, Size: 1076 bytes --]

On Mon, 2007-04-16 at 12:34 +0200, Miklos Szeredi wrote:
> Currently one of the difficulties with mount propagations is that
> there's no way to know the current state of the propagation tree.
> 
> Has anyone thought about how this info could be queried from
> userspace?

I am attaching two patches that I had done way back in Oct 2006 
with Al Viro. I had sent these patches to Al Viro. But I forgot to
follow them up, I guess so did Al Viro.

The first patch disambiguates multiple mount-instances of the same
filesystem (or part of the same filesystem), by introducing a new
interface /proc/mounts_new. 

The second patch introduces a new proc interface that exposes all the
propagation trees within a namespace.  It does not show propagated
mounts residing in a different namespace (for privacy reasons). Maybe
one could modify the patch a little, to allow it; if the user has
root priviledges. 

RP

PS: Sorry these are attachments instead of inline patches. I am scared
of inlining in evolution. If needed I can send inline patches through
mutt.

> 
> Thanks,
> Miklos

[-- Attachment #2: mounts.patch --]
[-- Type: text/x-patch, Size: 12207 bytes --]

This patch disambiguates multiple mount-instances of the same
filesystem (or part of the same filesystem), by introducing a new
interface /proc/mounts_new. The interface has the following format.

------------------------------------------------------------
FSID  mntpt  root-dentry  fstype fs-options
------------------------------------------------------------

NOTE: root-dentry is the path to the dentry w.r.t to the root dentry of the
same filesystem.

for example: lets say we attempt the following commands
mount --bind /var /mnt
mount --bind /mnt/tmp /tmp1

'cat /proc/mounts' shows the following:
/dev/root /mnt ext2 rw 0 0
/dev/root /tmp1 ext2 rw 0 0

NOTE: The above mount entries, do not indicate that /tmp1 contains the same
directory tree as /var/tmp.

But 'cat /proc/mounts_new' shows us the following:
0x6200 /mnt /var ext2 rw 0 0
0x6200 /tmp1 /var/tmp ext2 rw 0 0

The above entries clearly indicates that /var/tmp directory of the ext2
filesystem with fsid=0x6200 is the directory tree that resides under /tmp1

Signed-off-by: Ram Pai <linuxram-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>

---
 fs/dcache.c              |   53 ++++++++++++++++++++++++++++++++
 fs/namespace.c           |   35 ++++++++++++++++++---
 fs/proc/base.c           |   32 +++++++++++++++++--
 fs/proc/proc_misc.c      |    1 
 fs/seq_file.c            |   77 ++++++++++++++++++++++++++++++++++-------------
 include/linux/dcache.h   |    1 
 include/linux/seq_file.h |    1 
 7 files changed, 172 insertions(+), 28 deletions(-)

Index: linux-2.6.17.10/fs/proc/base.c
===================================================================
--- linux-2.6.17.10.orig/fs/proc/base.c
+++ linux-2.6.17.10/fs/proc/base.c
@@ -104,6 +104,7 @@ enum pid_directory_inos {
 	PROC_TGID_MAPS,
 	PROC_TGID_NUMA_MAPS,
 	PROC_TGID_MOUNTS,
+	PROC_TGID_MOUNTS_NEW,
 	PROC_TGID_MOUNTSTATS,
 	PROC_TGID_WCHAN,
 #ifdef CONFIG_MMU
@@ -145,6 +146,7 @@ enum pid_directory_inos {
 	PROC_TID_MAPS,
 	PROC_TID_NUMA_MAPS,
 	PROC_TID_MOUNTS,
+	PROC_TID_MOUNTS_NEW,
 	PROC_TID_MOUNTSTATS,
 	PROC_TID_WCHAN,
 #ifdef CONFIG_MMU
@@ -203,6 +205,7 @@ static struct pid_entry tgid_base_stuff[
 	E(PROC_TGID_ROOT,      "root",    S_IFLNK|S_IRWXUGO),
 	E(PROC_TGID_EXE,       "exe",     S_IFLNK|S_IRWXUGO),
 	E(PROC_TGID_MOUNTS,    "mounts",  S_IFREG|S_IRUGO),
+	E(PROC_TGID_MOUNTS_NEW,"mounts_new",  S_IFREG|S_IRUGO),
 	E(PROC_TGID_MOUNTSTATS, "mountstats", S_IFREG|S_IRUSR),
 #ifdef CONFIG_MMU
 	E(PROC_TGID_SMAPS,     "smaps",   S_IFREG|S_IRUGO),
@@ -246,6 +249,7 @@ static struct pid_entry tid_base_stuff[]
 	E(PROC_TID_ROOT,       "root",    S_IFLNK|S_IRWXUGO),
 	E(PROC_TID_EXE,        "exe",     S_IFLNK|S_IRWXUGO),
 	E(PROC_TID_MOUNTS,     "mounts",  S_IFREG|S_IRUGO),
+	E(PROC_TID_MOUNTS_NEW, "mounts_new",  S_IFREG|S_IRUGO),
 #ifdef CONFIG_MMU
 	E(PROC_TID_SMAPS,      "smaps",   S_IFREG|S_IRUGO),
 #endif
@@ -692,13 +696,13 @@ static struct file_operations proc_smaps
 };
 #endif
 
-extern struct seq_operations mounts_op;
 struct proc_mounts {
 	struct seq_file m;
 	int event;
 };
 
-static int mounts_open(struct inode *inode, struct file *file)
+static int __mounts_open(struct inode *inode, struct file *file,
+			struct seq_operations *mounts_op)
 {
 	struct task_struct *task = proc_task(inode);
 	struct namespace *namespace;
@@ -716,7 +720,7 @@ static int mounts_open(struct inode *ino
 		p = kmalloc(sizeof(struct proc_mounts), GFP_KERNEL);
 		if (p) {
 			file->private_data = &p->m;
-			ret = seq_open(file, &mounts_op);
+			ret = seq_open(file, mounts_op);
 			if (!ret) {
 				p->m.private = namespace;
 				p->event = namespace->event;
@@ -729,6 +733,16 @@ static int mounts_open(struct inode *ino
 	return ret;
 }
 
+extern struct seq_operations mounts_op, mounts_new_op;
+static int mounts_open(struct inode *inode, struct file *file)
+{
+	return (__mounts_open(inode, file, &mounts_op));
+}
+static int mounts_new_open(struct inode *inode, struct file *file)
+{
+	return __mounts_open(inode, file, &mounts_new_op);
+}
+
 static int mounts_release(struct inode *inode, struct file *file)
 {
 	struct seq_file *m = file->private_data;
@@ -763,6 +777,14 @@ static struct file_operations proc_mount
 	.poll		= mounts_poll,
 };
 
+static struct file_operations proc_mounts_new_operations = {
+	.open		= mounts_new_open,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= mounts_release,
+	.poll		= mounts_poll,
+};
+
 extern struct seq_operations mountstats_op;
 static int mountstats_open(struct inode *inode, struct file *file)
 {
@@ -1799,6 +1821,10 @@ static struct dentry *proc_pident_lookup
 		case PROC_TGID_MOUNTS:
 			inode->i_fop = &proc_mounts_operations;
 			break;
+		case PROC_TID_MOUNTS_NEW:
+		case PROC_TGID_MOUNTS_NEW:
+			inode->i_fop = &proc_mounts_new_operations;
+			break;
 #ifdef CONFIG_MMU
 		case PROC_TID_SMAPS:
 		case PROC_TGID_SMAPS:
Index: linux-2.6.17.10/fs/dcache.c
===================================================================
--- linux-2.6.17.10.orig/fs/dcache.c
+++ linux-2.6.17.10/fs/dcache.c
@@ -1477,6 +1477,59 @@ char * d_path(struct dentry *dentry, str
 	return res;
 }
 
+static inline int prepend(char **buffer, int *buflen, const char *str,
+					int namelen)
+{
+	if ((*buflen -= namelen) < 0)
+		return 1;
+	*buffer -= namelen;
+	memcpy(*buffer, str, namelen);
+	return 0;
+}
+
+/*
+ * write full pathname into buffer and return start of pathname.
+ * If @vfsmnt is not specified return the path relative to the
+ * its filesystem's root.
+ */
+char * dentry_path(struct dentry *dentry, char *buf, int buflen)
+{
+	char * end = buf+buflen;
+	char * retval;
+
+	spin_lock(&dcache_lock);
+	prepend(&end, &buflen, "\0", 1);
+	if (!IS_ROOT(dentry) && d_unhashed(dentry)) {
+		if (prepend(&end, &buflen, "//deleted", 10))
+			goto Elong;
+	}
+	/* Get '/' right */
+	retval = end-1;
+	*retval = '/';
+
+	for (;;) {
+		struct dentry * parent;
+		if (IS_ROOT(dentry))
+			break;
+
+		parent = dentry->d_parent;
+		prefetch(parent);
+
+		if (prepend(&end, &buflen, dentry->d_name.name,
+				dentry->d_name.len) ||
+	            prepend(&end, &buflen, "/", 1))
+			goto Elong;
+
+		retval = end;
+		dentry = parent;
+	}
+	spin_unlock(&dcache_lock);
+	return retval;
+Elong:
+	spin_unlock(&dcache_lock);
+	return ERR_PTR(-ENAMETOOLONG);
+}
+
 /*
  * NOTE! The user-level library version returns a
  * character pointer. The kernel system call just
Index: linux-2.6.17.10/fs/seq_file.c
===================================================================
--- linux-2.6.17.10.orig/fs/seq_file.c
+++ linux-2.6.17.10/fs/seq_file.c
@@ -338,38 +338,75 @@ int seq_printf(struct seq_file *m, const
 }
 EXPORT_SYMBOL(seq_printf);
 
-int seq_path(struct seq_file *m,
-	     struct vfsmount *mnt, struct dentry *dentry,
+static inline char *mangle_path(char *s, char *p, char *esc)
+{
+	while (s <= p) {
+		char c = *p++;
+		if (!c) {
+			return s;
+		} else if (!strchr(esc, c)) {
+			*s++ = c;
+		} else if (s + 4 > p) {
+			break;
+		} else {
+			*s++ = '\\';
+			*s++ = '0' + ((c & 0300) >> 6);
+			*s++ = '0' + ((c & 070) >> 3);
+			*s++ = '0' + (c & 07);
+		}
+	}
+	return NULL;
+}
+
+/*
+ * return the absolute path of 'dentry' residing in mount 'mnt'.
+ */
+int seq_path(struct seq_file *m, struct vfsmount *mnt, struct dentry *dentry,
 	     char *esc)
 {
+	char *p = NULL;
 	if (m->count < m->size) {
 		char *s = m->buf + m->count;
-		char *p = d_path(dentry, mnt, s, m->size - m->count);
+		p = d_path(dentry, mnt, s, m->size - m->count);
 		if (!IS_ERR(p)) {
-			while (s <= p) {
-				char c = *p++;
-				if (!c) {
-					p = m->buf + m->count;
-					m->count = s - m->buf;
-					return s - p;
-				} else if (!strchr(esc, c)) {
-					*s++ = c;
-				} else if (s + 4 > p) {
-					break;
-				} else {
-					*s++ = '\\';
-					*s++ = '0' + ((c & 0300) >> 6);
-					*s++ = '0' + ((c & 070) >> 3);
-					*s++ = '0' + (c & 07);
-				}
+			s = mangle_path(s, p, esc);
+			if (s) {
+				p = m->buf + m->count;
+				m->count = s - m->buf;
+				return s - p;
 			}
 		}
 	}
 	m->count = m->size;
-	return -1;
+	return p == ERR_PTR(-ENAMETOOLONG) ? 0 : -1;
 }
+
 EXPORT_SYMBOL(seq_path);
 
+/*
+ * returns the path of the 'dentry' from the root of its filesystem.
+ */
+int seq_dentry(struct seq_file *m, struct dentry *dentry, char *esc)
+{
+	char *p = NULL;
+	if (m->count < m->size) {
+		char *s = m->buf + m->count;
+		p = dentry_path(dentry, s, m->size - m->count);
+		if (!IS_ERR(p)) {
+			s = mangle_path(s, p, esc);
+			if (s) {
+				p = m->buf + m->count;
+				m->count = s - m->buf;
+				return s - p;
+			}
+		}
+	}
+	m->count = m->size;
+	return p == ERR_PTR(-ENAMETOOLONG) ? 0 : -1;
+}
+
+EXPORT_SYMBOL(seq_dentry);
+
 static void *single_start(struct seq_file *p, loff_t *pos)
 {
 	return NULL + (*pos == 0);
Index: linux-2.6.17.10/fs/proc/proc_misc.c
===================================================================
--- linux-2.6.17.10.orig/fs/proc/proc_misc.c
+++ linux-2.6.17.10/fs/proc/proc_misc.c
@@ -675,6 +675,7 @@ void __init proc_misc_init(void)
 		create_proc_read_entry(p->name, 0, NULL, p->read_proc, NULL);
 
 	proc_symlink("mounts", NULL, "self/mounts");
+	proc_symlink("mounts_new", NULL, "self/mounts_new");
 
 	/* And now for trickier ones */
 	entry = create_proc_entry("kmsg", S_IRUSR, &proc_root);
Index: linux-2.6.17.10/fs/namespace.c
===================================================================
--- linux-2.6.17.10.orig/fs/namespace.c
+++ linux-2.6.17.10/fs/namespace.c
@@ -349,7 +349,7 @@ static inline void mangle(struct seq_fil
 	seq_escape(m, s, " \t\n\\");
 }
 
-static int show_vfsmnt(struct seq_file *m, void *v)
+static int show_options(struct seq_file *m, void *v)
 {
 	struct vfsmount *mnt = v;
 	int err = 0;
@@ -372,10 +372,6 @@ static int show_vfsmnt(struct seq_file *
 	};
 	struct proc_fs_info *fs_infop;
 
-	mangle(m, mnt->mnt_devname ? mnt->mnt_devname : "none");
-	seq_putc(m, ' ');
-	seq_path(m, mnt, mnt->mnt_root, " \t\n\\");
-	seq_putc(m, ' ');
 	mangle(m, mnt->mnt_sb->s_type->name);
 	seq_puts(m, mnt->mnt_sb->s_flags & MS_RDONLY ? " ro" : " rw");
 	for (fs_infop = fs_info; fs_infop->flag; fs_infop++) {
@@ -392,6 +388,28 @@ static int show_vfsmnt(struct seq_file *
 	return err;
 }
 
+static int show_vfsmnt(struct seq_file *m, void *v)
+{
+	struct vfsmount *mnt = v;
+	mangle(m, mnt->mnt_devname ? mnt->mnt_devname : "none");
+	seq_putc(m, ' ');
+	seq_path(m, mnt, mnt->mnt_root, " \t\n\\");
+	seq_putc(m, ' ');
+	return show_options(m, v);
+}
+
+static int show_vfsmnt_new(struct seq_file *m, void *v)
+{
+	struct vfsmount *mnt = v;
+	seq_printf(m, "0x%x", new_encode_dev(mnt->mnt_sb->s_dev));
+	seq_putc(m, ' ');
+	seq_path(m, mnt, mnt->mnt_root, " \t\n\\");
+	seq_putc(m, ' ');
+	seq_dentry(m, mnt->mnt_root, " \t\n\\");
+	seq_putc(m, ' ');
+	return show_options(m, v);
+}
+
 struct seq_operations mounts_op = {
 	.start	= m_start,
 	.next	= m_next,
@@ -399,6 +417,13 @@ struct seq_operations mounts_op = {
 	.show	= show_vfsmnt
 };
 
+struct seq_operations mounts_new_op = {
+	.start	= m_start,
+	.next	= m_next,
+	.stop	= m_stop,
+	.show	= show_vfsmnt_new
+};
+
 static int show_vfsstat(struct seq_file *m, void *v)
 {
 	struct vfsmount *mnt = v;
Index: linux-2.6.17.10/include/linux/dcache.h
===================================================================
--- linux-2.6.17.10.orig/include/linux/dcache.h
+++ linux-2.6.17.10/include/linux/dcache.h
@@ -281,6 +281,7 @@ extern struct dentry * d_hash_and_lookup
 extern int d_validate(struct dentry *, struct dentry *);
 
 extern char * d_path(struct dentry *, struct vfsmount *, char *, int);
+extern char * dentry_path(struct dentry *, char *, int);
   
 /* Allocation counts.. */
 
Index: linux-2.6.17.10/include/linux/seq_file.h
===================================================================
--- linux-2.6.17.10.orig/include/linux/seq_file.h
+++ linux-2.6.17.10/include/linux/seq_file.h
@@ -43,6 +43,7 @@ int seq_printf(struct seq_file *, const 
 	__attribute__ ((format (printf,2,3)));
 
 int seq_path(struct seq_file *, struct vfsmount *, struct dentry *, char *);
+int seq_dentry(struct seq_file *, struct dentry *, char *);
 
 int single_open(struct file *, int (*)(struct seq_file *, void *), void *);
 int single_release(struct inode *, struct file *);

[-- Attachment #3: propagation.patch --]
[-- Type: text/x-patch, Size: 7720 bytes --]

This patch introduces a new proc interface that exposes all the propagation 
trees within the namespace.

It walks through each off the mounts in the namespace, and prints the following information.

mount-id: a unique mount identifier
dev-id : the unique device used to identify the device containing the filesystem
path-from-root: mount point of the mount from /
path-from-root-of-its-sb: path from its own root dentry.
propagation-flag: SHARED, SLAVE, UNBINDABLE, PRIVATE
peer-mount-id: the mount-id of its peer mount (if this mount is shared)
master-mount-id: the mount-id of its master mount (if this mount is slave)

Using the above information one could easily write a script that can
draw all the propagation trees in the namespace.


Example:
Here is a sample output of cat /proc/$$/mounts_propagation

0xa917800 0x1 / / PRIVATE
0xa917200 0x6200 / / PRIVATE
0xa917180 0x3 /proc / PRIVATE
0xa917f80 0xa /dev/pts / PRIVATE
0xa917100 0x6210 /mnt / SHARED peer:0xa917100
0xa917f00 0x6210 /tmp /1 SLAVE master:0xa917100
0xa917900 0x6220 /mnt/2 / SHARED peer:0xa917900

line 5 indicates that the mount with id 0xa917100 is mounted at /mnt is shared
and it is the only mount in its peer group.

line 6 indicates that the mount with id 0xa917f00 is mounted at /tmp, its 
root is the dentry 1 present under its root directory. This mount is a
slave mount and its master is the mount with id 0xa917100.

line 7 indicates that the mount with id 0xa917900 is mounted at /mnt/2, its 
root is the dentry / of its filesystem. This mount is a
shared and it is the only mount in its peer group.

one could write a script which runs through these lines and draws 4
individual satellite mounts and two propagation trees, the first propagation
tree has a shared mount and a slave mount.  and the second propagation tree has
just one shared mount.

	
Signed-off-by: Ram Pai <linuxram-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>
---
 fs/namespace.c |   42 ++++++++++++++++++++++++++++++++++++++++++
 fs/pnode.c     |    6 ------
 fs/pnode.h     |    6 ++++++
 fs/proc/base.c |   22 +++++++++++++++++++++-
 4 files changed, 69 insertions(+), 7 deletions(-)

Index: linux-2.6.17.10/fs/namespace.c
===================================================================
--- linux-2.6.17.10.orig/fs/namespace.c
+++ linux-2.6.17.10/fs/namespace.c
@@ -410,6 +410,41 @@ static int show_vfsmnt_new(struct seq_fi
 	return show_options(m, v);
 }
 
+static int show_vfsmnt_propagation(struct seq_file *m, void *v)
+{
+	struct vfsmount *mnt = v;
+	seq_printf(m, "0x%x", (int)mnt);
+	seq_putc(m, ' ');
+	seq_printf(m, "0x%x", new_encode_dev(mnt->mnt_sb->s_dev));
+	seq_putc(m, ' ');
+	seq_path(m, mnt, mnt->mnt_root, " \t\n\\");
+	seq_putc(m, ' ');
+	seq_dentry(m, mnt->mnt_root, " \t\n\\");
+	seq_putc(m, ' ');
+
+	if (IS_MNT_SHARED(mnt)) {
+		seq_printf(m, "%s ", "SHARED");
+		if (IS_MNT_SLAVE(mnt)) {
+			seq_printf(m, "%s ", "SLAVE");
+		}
+	} else if (IS_MNT_SLAVE(mnt)) {
+		seq_printf(m, "%s ", "SLAVE");
+	} else if (IS_MNT_UNBINDABLE(mnt)) {
+		seq_printf(m, "%s ", "UNBINDABLE");
+	} else {
+		seq_printf(m, "%s ", "PRIVATE");
+	}
+
+	if (IS_MNT_SHARED(mnt)) {
+		seq_printf(m, "peer:0x%x ", (int)next_peer(mnt));
+	}
+	if (IS_MNT_SLAVE(mnt)) {
+		seq_printf(m, "master:0x%x ", (int)mnt->mnt_master);
+	}
+	seq_puts(m, "\n");
+	return 0;
+}
+
 struct seq_operations mounts_op = {
 	.start	= m_start,
 	.next	= m_next,
@@ -424,6 +459,13 @@ struct seq_operations mounts_new_op = {
 	.show	= show_vfsmnt_new
 };
 
+struct seq_operations mounts_propagation_op = {
+	.start	= m_start,
+	.next	= m_next,
+	.stop	= m_stop,
+	.show	= show_vfsmnt_propagation
+};
+
 static int show_vfsstat(struct seq_file *m, void *v)
 {
 	struct vfsmount *mnt = v;
Index: linux-2.6.17.10/fs/proc/base.c
===================================================================
--- linux-2.6.17.10.orig/fs/proc/base.c
+++ linux-2.6.17.10/fs/proc/base.c
@@ -105,6 +105,7 @@ enum pid_directory_inos {
 	PROC_TGID_NUMA_MAPS,
 	PROC_TGID_MOUNTS,
 	PROC_TGID_MOUNTS_NEW,
+	PROC_TGID_MOUNTS_PROPAGATION,
 	PROC_TGID_MOUNTSTATS,
 	PROC_TGID_WCHAN,
 #ifdef CONFIG_MMU
@@ -146,6 +147,7 @@ enum pid_directory_inos {
 	PROC_TID_MAPS,
 	PROC_TID_NUMA_MAPS,
 	PROC_TID_MOUNTS,
+	PROC_TID_MOUNTS_PROPAGATION,
 	PROC_TID_MOUNTS_NEW,
 	PROC_TID_MOUNTSTATS,
 	PROC_TID_WCHAN,
@@ -206,6 +208,7 @@ static struct pid_entry tgid_base_stuff[
 	E(PROC_TGID_EXE,       "exe",     S_IFLNK|S_IRWXUGO),
 	E(PROC_TGID_MOUNTS,    "mounts",  S_IFREG|S_IRUGO),
 	E(PROC_TGID_MOUNTS_NEW,"mounts_new",  S_IFREG|S_IRUGO),
+	E(PROC_TGID_MOUNTS_PROPAGATION,"mounts_propagation",  S_IFREG|S_IRUGO),
 	E(PROC_TGID_MOUNTSTATS, "mountstats", S_IFREG|S_IRUSR),
 #ifdef CONFIG_MMU
 	E(PROC_TGID_SMAPS,     "smaps",   S_IFREG|S_IRUGO),
@@ -250,6 +253,7 @@ static struct pid_entry tid_base_stuff[]
 	E(PROC_TID_EXE,        "exe",     S_IFLNK|S_IRWXUGO),
 	E(PROC_TID_MOUNTS,     "mounts",  S_IFREG|S_IRUGO),
 	E(PROC_TID_MOUNTS_NEW, "mounts_new",  S_IFREG|S_IRUGO),
+	E(PROC_TID_MOUNTS_PROPAGATION,"mounts_propagation",  S_IFREG|S_IRUGO),
 #ifdef CONFIG_MMU
 	E(PROC_TID_SMAPS,      "smaps",   S_IFREG|S_IRUGO),
 #endif
@@ -733,7 +737,7 @@ static int __mounts_open(struct inode *i
 	return ret;
 }
 
-extern struct seq_operations mounts_op, mounts_new_op;
+extern struct seq_operations mounts_op, mounts_new_op, mounts_propagation_op;
 static int mounts_open(struct inode *inode, struct file *file)
 {
 	return (__mounts_open(inode, file, &mounts_op));
@@ -742,6 +746,10 @@ static int mounts_new_open(struct inode 
 {
 	return __mounts_open(inode, file, &mounts_new_op);
 }
+static int mounts_propagation_open(struct inode *inode, struct file *file)
+{
+	return __mounts_open(inode, file, &mounts_propagation_op);
+}
 
 static int mounts_release(struct inode *inode, struct file *file)
 {
@@ -785,6 +793,14 @@ static struct file_operations proc_mount
 	.poll		= mounts_poll,
 };
 
+static struct file_operations proc_propagation_operations = {
+	.open		= mounts_propagation_open,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= mounts_release,
+	.poll		= mounts_poll,
+};
+
 extern struct seq_operations mountstats_op;
 static int mountstats_open(struct inode *inode, struct file *file)
 {
@@ -1825,6 +1841,10 @@ static struct dentry *proc_pident_lookup
 		case PROC_TGID_MOUNTS_NEW:
 			inode->i_fop = &proc_mounts_new_operations;
 			break;
+		case PROC_TID_MOUNTS_PROPAGATION:
+		case PROC_TGID_MOUNTS_PROPAGATION:
+			inode->i_fop = &proc_propagation_operations;
+			break;
 #ifdef CONFIG_MMU
 		case PROC_TID_SMAPS:
 		case PROC_TGID_SMAPS:
Index: linux-2.6.17.10/fs/pnode.c
===================================================================
--- linux-2.6.17.10.orig/fs/pnode.c
+++ linux-2.6.17.10/fs/pnode.c
@@ -11,12 +11,6 @@
 #include <linux/fs.h>
 #include "pnode.h"
 
-/* return the next shared peer mount of @p */
-static inline struct vfsmount *next_peer(struct vfsmount *p)
-{
-	return list_entry(p->mnt_share.next, struct vfsmount, mnt_share);
-}
-
 static inline struct vfsmount *first_slave(struct vfsmount *p)
 {
 	return list_entry(p->mnt_slave_list.next, struct vfsmount, mnt_slave);
Index: linux-2.6.17.10/fs/pnode.h
===================================================================
--- linux-2.6.17.10.orig/fs/pnode.h
+++ linux-2.6.17.10/fs/pnode.h
@@ -29,6 +29,12 @@ static inline void set_mnt_shared(struct
 	mnt->mnt_flags |= MNT_SHARED;
 }
 
+/* return the next shared peer mount of @p */
+static inline struct vfsmount *next_peer(struct vfsmount *p)
+{
+	return list_entry(p->mnt_share.next, struct vfsmount, mnt_share);
+}
+
 void change_mnt_propagation(struct vfsmount *, int);
 int propagate_mnt(struct vfsmount *, struct dentry *, struct vfsmount *,
 		struct list_head *);

Re: How to query mount propagation state?

[Serge E. Hallyn]

Quoting Ram Pai (linuxram@us.ibm.com):
> On Mon, 2007-04-16 at 12:34 +0200, Miklos Szeredi wrote:
> > Currently one of the difficulties with mount propagations is that
> > there's no way to know the current state of the propagation tree.
> > 
> > Has anyone thought about how this info could be queried from
> > userspace?
> 
> I am attaching two patches that I had done way back in Oct 2006 
> with Al Viro. I had sent these patches to Al Viro. But I forgot to
> follow them up, I guess so did Al Viro.
> 
> The first patch disambiguates multiple mount-instances of the same
> filesystem (or part of the same filesystem), by introducing a new
> interface /proc/mounts_new. 
> 
> The second patch introduces a new proc interface that exposes all the
> propagation trees within a namespace.  It does not show propagated
> mounts residing in a different namespace (for privacy reasons). Maybe
> one could modify the patch a little, to allow it; if the user has
> root priviledges. 
> 
> RP
> 
> PS: Sorry these are attachments instead of inline patches. I am scared
> of inlining in evolution. If needed I can send inline patches through
> mutt.
> 
> > 
> > Thanks,
> > Miklos

> This patch disambiguates multiple mount-instances of the same
> filesystem (or part of the same filesystem), by introducing a new
> interface /proc/mounts_new. The interface has the following format.
> 
> ------------------------------------------------------------
> FSID  mntpt  root-dentry  fstype fs-options
> ------------------------------------------------------------
> 
> NOTE: root-dentry is the path to the dentry w.r.t to the root dentry of the
> same filesystem.
> 
> for example: lets say we attempt the following commands
> mount --bind /var /mnt
> mount --bind /mnt/tmp /tmp1
> 
> 'cat /proc/mounts' shows the following:
> /dev/root /mnt ext2 rw 0 0
> /dev/root /tmp1 ext2 rw 0 0
> 
> NOTE: The above mount entries, do not indicate that /tmp1 contains the same
> directory tree as /var/tmp.
> 
> But 'cat /proc/mounts_new' shows us the following:
> 0x6200 /mnt /var ext2 rw 0 0
> 0x6200 /tmp1 /var/tmp ext2 rw 0 0
> 
> The above entries clearly indicates that /var/tmp directory of the ext2
> filesystem with fsid=0x6200 is the directory tree that resides under /tmp1
> 
> Signed-off-by: Ram Pai <linuxram@us.ibm.com>
> 
> ---
>  fs/dcache.c              |   53 ++++++++++++++++++++++++++++++++
>  fs/namespace.c           |   35 ++++++++++++++++++---
>  fs/proc/base.c           |   32 +++++++++++++++++--
>  fs/proc/proc_misc.c      |    1 
>  fs/seq_file.c            |   77 ++++++++++++++++++++++++++++++++++-------------
>  include/linux/dcache.h   |    1 
>  include/linux/seq_file.h |    1 
>  7 files changed, 172 insertions(+), 28 deletions(-)
> 
> Index: linux-2.6.17.10/fs/proc/base.c
> ===================================================================
> --- linux-2.6.17.10.orig/fs/proc/base.c
> +++ linux-2.6.17.10/fs/proc/base.c
> @@ -104,6 +104,7 @@ enum pid_directory_inos {
>  	PROC_TGID_MAPS,
>  	PROC_TGID_NUMA_MAPS,
>  	PROC_TGID_MOUNTS,
> +	PROC_TGID_MOUNTS_NEW,
>  	PROC_TGID_MOUNTSTATS,
>  	PROC_TGID_WCHAN,
>  #ifdef CONFIG_MMU
> @@ -145,6 +146,7 @@ enum pid_directory_inos {
>  	PROC_TID_MAPS,
>  	PROC_TID_NUMA_MAPS,
>  	PROC_TID_MOUNTS,
> +	PROC_TID_MOUNTS_NEW,
>  	PROC_TID_MOUNTSTATS,
>  	PROC_TID_WCHAN,
>  #ifdef CONFIG_MMU
> @@ -203,6 +205,7 @@ static struct pid_entry tgid_base_stuff[
>  	E(PROC_TGID_ROOT,      "root",    S_IFLNK|S_IRWXUGO),
>  	E(PROC_TGID_EXE,       "exe",     S_IFLNK|S_IRWXUGO),
>  	E(PROC_TGID_MOUNTS,    "mounts",  S_IFREG|S_IRUGO),
> +	E(PROC_TGID_MOUNTS_NEW,"mounts_new",  S_IFREG|S_IRUGO),
>  	E(PROC_TGID_MOUNTSTATS, "mountstats", S_IFREG|S_IRUSR),
>  #ifdef CONFIG_MMU
>  	E(PROC_TGID_SMAPS,     "smaps",   S_IFREG|S_IRUGO),
> @@ -246,6 +249,7 @@ static struct pid_entry tid_base_stuff[]
>  	E(PROC_TID_ROOT,       "root",    S_IFLNK|S_IRWXUGO),
>  	E(PROC_TID_EXE,        "exe",     S_IFLNK|S_IRWXUGO),
>  	E(PROC_TID_MOUNTS,     "mounts",  S_IFREG|S_IRUGO),
> +	E(PROC_TID_MOUNTS_NEW, "mounts_new",  S_IFREG|S_IRUGO),
>  #ifdef CONFIG_MMU
>  	E(PROC_TID_SMAPS,      "smaps",   S_IFREG|S_IRUGO),
>  #endif
> @@ -692,13 +696,13 @@ static struct file_operations proc_smaps
>  };
>  #endif
> 
> -extern struct seq_operations mounts_op;
>  struct proc_mounts {
>  	struct seq_file m;
>  	int event;
>  };
> 
> -static int mounts_open(struct inode *inode, struct file *file)
> +static int __mounts_open(struct inode *inode, struct file *file,
> +			struct seq_operations *mounts_op)
>  {
>  	struct task_struct *task = proc_task(inode);
>  	struct namespace *namespace;
> @@ -716,7 +720,7 @@ static int mounts_open(struct inode *ino
>  		p = kmalloc(sizeof(struct proc_mounts), GFP_KERNEL);
>  		if (p) {
>  			file->private_data = &p->m;
> -			ret = seq_open(file, &mounts_op);
> +			ret = seq_open(file, mounts_op);
>  			if (!ret) {
>  				p->m.private = namespace;
>  				p->event = namespace->event;
> @@ -729,6 +733,16 @@ static int mounts_open(struct inode *ino
>  	return ret;
>  }
> 
> +extern struct seq_operations mounts_op, mounts_new_op;
> +static int mounts_open(struct inode *inode, struct file *file)
> +{
> +	return (__mounts_open(inode, file, &mounts_op));
> +}
> +static int mounts_new_open(struct inode *inode, struct file *file)
> +{
> +	return __mounts_open(inode, file, &mounts_new_op);
> +}
> +
>  static int mounts_release(struct inode *inode, struct file *file)
>  {
>  	struct seq_file *m = file->private_data;
> @@ -763,6 +777,14 @@ static struct file_operations proc_mount
>  	.poll		= mounts_poll,
>  };
> 
> +static struct file_operations proc_mounts_new_operations = {
> +	.open		= mounts_new_open,
> +	.read		= seq_read,
> +	.llseek		= seq_lseek,
> +	.release	= mounts_release,
> +	.poll		= mounts_poll,
> +};
> +
>  extern struct seq_operations mountstats_op;
>  static int mountstats_open(struct inode *inode, struct file *file)
>  {
> @@ -1799,6 +1821,10 @@ static struct dentry *proc_pident_lookup
>  		case PROC_TGID_MOUNTS:
>  			inode->i_fop = &proc_mounts_operations;
>  			break;
> +		case PROC_TID_MOUNTS_NEW:
> +		case PROC_TGID_MOUNTS_NEW:
> +			inode->i_fop = &proc_mounts_new_operations;
> +			break;
>  #ifdef CONFIG_MMU
>  		case PROC_TID_SMAPS:
>  		case PROC_TGID_SMAPS:
> Index: linux-2.6.17.10/fs/dcache.c
> ===================================================================
> --- linux-2.6.17.10.orig/fs/dcache.c
> +++ linux-2.6.17.10/fs/dcache.c
> @@ -1477,6 +1477,59 @@ char * d_path(struct dentry *dentry, str
>  	return res;
>  }
> 
> +static inline int prepend(char **buffer, int *buflen, const char *str,
> +					int namelen)
> +{
> +	if ((*buflen -= namelen) < 0)
> +		return 1;
> +	*buffer -= namelen;
> +	memcpy(*buffer, str, namelen);
> +	return 0;
> +}
> +
> +/*
> + * write full pathname into buffer and return start of pathname.
> + * If @vfsmnt is not specified return the path relative to the
> + * its filesystem's root.
> + */
> +char * dentry_path(struct dentry *dentry, char *buf, int buflen)
> +{
> +	char * end = buf+buflen;
> +	char * retval;
> +
> +	spin_lock(&dcache_lock);
> +	prepend(&end, &buflen, "\0", 1);
> +	if (!IS_ROOT(dentry) && d_unhashed(dentry)) {
> +		if (prepend(&end, &buflen, "//deleted", 10))
> +			goto Elong;
> +	}
> +	/* Get '/' right */
> +	retval = end-1;
> +	*retval = '/';
> +
> +	for (;;) {
> +		struct dentry * parent;
> +		if (IS_ROOT(dentry))
> +			break;
> +
> +		parent = dentry->d_parent;
> +		prefetch(parent);
> +
> +		if (prepend(&end, &buflen, dentry->d_name.name,
> +				dentry->d_name.len) ||
> +	            prepend(&end, &buflen, "/", 1))
> +			goto Elong;
> +
> +		retval = end;
> +		dentry = parent;
> +	}
> +	spin_unlock(&dcache_lock);
> +	return retval;
> +Elong:
> +	spin_unlock(&dcache_lock);
> +	return ERR_PTR(-ENAMETOOLONG);
> +}
> +
>  /*
>   * NOTE! The user-level library version returns a
>   * character pointer. The kernel system call just
> Index: linux-2.6.17.10/fs/seq_file.c
> ===================================================================
> --- linux-2.6.17.10.orig/fs/seq_file.c
> +++ linux-2.6.17.10/fs/seq_file.c
> @@ -338,38 +338,75 @@ int seq_printf(struct seq_file *m, const
>  }
>  EXPORT_SYMBOL(seq_printf);
> 
> -int seq_path(struct seq_file *m,
> -	     struct vfsmount *mnt, struct dentry *dentry,
> +static inline char *mangle_path(char *s, char *p, char *esc)
> +{
> +	while (s <= p) {
> +		char c = *p++;
> +		if (!c) {
> +			return s;
> +		} else if (!strchr(esc, c)) {
> +			*s++ = c;
> +		} else if (s + 4 > p) {
> +			break;
> +		} else {
> +			*s++ = '\\';
> +			*s++ = '0' + ((c & 0300) >> 6);
> +			*s++ = '0' + ((c & 070) >> 3);
> +			*s++ = '0' + (c & 07);
> +		}
> +	}
> +	return NULL;
> +}
> +
> +/*
> + * return the absolute path of 'dentry' residing in mount 'mnt'.
> + */
> +int seq_path(struct seq_file *m, struct vfsmount *mnt, struct dentry *dentry,
>  	     char *esc)
>  {
> +	char *p = NULL;
>  	if (m->count < m->size) {
>  		char *s = m->buf + m->count;
> -		char *p = d_path(dentry, mnt, s, m->size - m->count);
> +		p = d_path(dentry, mnt, s, m->size - m->count);
>  		if (!IS_ERR(p)) {
> -			while (s <= p) {
> -				char c = *p++;
> -				if (!c) {
> -					p = m->buf + m->count;
> -					m->count = s - m->buf;
> -					return s - p;
> -				} else if (!strchr(esc, c)) {
> -					*s++ = c;
> -				} else if (s + 4 > p) {
> -					break;
> -				} else {
> -					*s++ = '\\';
> -					*s++ = '0' + ((c & 0300) >> 6);
> -					*s++ = '0' + ((c & 070) >> 3);
> -					*s++ = '0' + (c & 07);
> -				}
> +			s = mangle_path(s, p, esc);
> +			if (s) {
> +				p = m->buf + m->count;
> +				m->count = s - m->buf;
> +				return s - p;
>  			}
>  		}
>  	}
>  	m->count = m->size;
> -	return -1;
> +	return p == ERR_PTR(-ENAMETOOLONG) ? 0 : -1;
>  }
> +
>  EXPORT_SYMBOL(seq_path);
> 
> +/*
> + * returns the path of the 'dentry' from the root of its filesystem.
> + */
> +int seq_dentry(struct seq_file *m, struct dentry *dentry, char *esc)
> +{
> +	char *p = NULL;
> +	if (m->count < m->size) {
> +		char *s = m->buf + m->count;
> +		p = dentry_path(dentry, s, m->size - m->count);
> +		if (!IS_ERR(p)) {
> +			s = mangle_path(s, p, esc);
> +			if (s) {
> +				p = m->buf + m->count;
> +				m->count = s - m->buf;
> +				return s - p;
> +			}
> +		}
> +	}
> +	m->count = m->size;
> +	return p == ERR_PTR(-ENAMETOOLONG) ? 0 : -1;
> +}
> +
> +EXPORT_SYMBOL(seq_dentry);
> +
>  static void *single_start(struct seq_file *p, loff_t *pos)
>  {
>  	return NULL + (*pos == 0);
> Index: linux-2.6.17.10/fs/proc/proc_misc.c
> ===================================================================
> --- linux-2.6.17.10.orig/fs/proc/proc_misc.c
> +++ linux-2.6.17.10/fs/proc/proc_misc.c
> @@ -675,6 +675,7 @@ void __init proc_misc_init(void)
>  		create_proc_read_entry(p->name, 0, NULL, p->read_proc, NULL);
> 
>  	proc_symlink("mounts", NULL, "self/mounts");
> +	proc_symlink("mounts_new", NULL, "self/mounts_new");
> 
>  	/* And now for trickier ones */
>  	entry = create_proc_entry("kmsg", S_IRUSR, &proc_root);
> Index: linux-2.6.17.10/fs/namespace.c
> ===================================================================
> --- linux-2.6.17.10.orig/fs/namespace.c
> +++ linux-2.6.17.10/fs/namespace.c
> @@ -349,7 +349,7 @@ static inline void mangle(struct seq_fil
>  	seq_escape(m, s, " \t\n\\");
>  }
> 
> -static int show_vfsmnt(struct seq_file *m, void *v)
> +static int show_options(struct seq_file *m, void *v)
>  {
>  	struct vfsmount *mnt = v;
>  	int err = 0;
> @@ -372,10 +372,6 @@ static int show_vfsmnt(struct seq_file *
>  	};
>  	struct proc_fs_info *fs_infop;
> 
> -	mangle(m, mnt->mnt_devname ? mnt->mnt_devname : "none");
> -	seq_putc(m, ' ');
> -	seq_path(m, mnt, mnt->mnt_root, " \t\n\\");
> -	seq_putc(m, ' ');
>  	mangle(m, mnt->mnt_sb->s_type->name);
>  	seq_puts(m, mnt->mnt_sb->s_flags & MS_RDONLY ? " ro" : " rw");
>  	for (fs_infop = fs_info; fs_infop->flag; fs_infop++) {
> @@ -392,6 +388,28 @@ static int show_vfsmnt(struct seq_file *
>  	return err;
>  }
> 
> +static int show_vfsmnt(struct seq_file *m, void *v)
> +{
> +	struct vfsmount *mnt = v;
> +	mangle(m, mnt->mnt_devname ? mnt->mnt_devname : "none");
> +	seq_putc(m, ' ');
> +	seq_path(m, mnt, mnt->mnt_root, " \t\n\\");
> +	seq_putc(m, ' ');
> +	return show_options(m, v);
> +}
> +
> +static int show_vfsmnt_new(struct seq_file *m, void *v)
> +{
> +	struct vfsmount *mnt = v;
> +	seq_printf(m, "0x%x", new_encode_dev(mnt->mnt_sb->s_dev));
> +	seq_putc(m, ' ');
> +	seq_path(m, mnt, mnt->mnt_root, " \t\n\\");
> +	seq_putc(m, ' ');
> +	seq_dentry(m, mnt->mnt_root, " \t\n\\");
> +	seq_putc(m, ' ');
> +	return show_options(m, v);
> +}
> +
>  struct seq_operations mounts_op = {
>  	.start	= m_start,
>  	.next	= m_next,
> @@ -399,6 +417,13 @@ struct seq_operations mounts_op = {
>  	.show	= show_vfsmnt
>  };
> 
> +struct seq_operations mounts_new_op = {
> +	.start	= m_start,
> +	.next	= m_next,
> +	.stop	= m_stop,
> +	.show	= show_vfsmnt_new
> +};
> +
>  static int show_vfsstat(struct seq_file *m, void *v)
>  {
>  	struct vfsmount *mnt = v;
> Index: linux-2.6.17.10/include/linux/dcache.h
> ===================================================================
> --- linux-2.6.17.10.orig/include/linux/dcache.h
> +++ linux-2.6.17.10/include/linux/dcache.h
> @@ -281,6 +281,7 @@ extern struct dentry * d_hash_and_lookup
>  extern int d_validate(struct dentry *, struct dentry *);
> 
>  extern char * d_path(struct dentry *, struct vfsmount *, char *, int);
> +extern char * dentry_path(struct dentry *, char *, int);
>    
>  /* Allocation counts.. */
> 
> Index: linux-2.6.17.10/include/linux/seq_file.h
> ===================================================================
> --- linux-2.6.17.10.orig/include/linux/seq_file.h
> +++ linux-2.6.17.10/include/linux/seq_file.h
> @@ -43,6 +43,7 @@ int seq_printf(struct seq_file *, const 
>  	__attribute__ ((format (printf,2,3)));
> 
>  int seq_path(struct seq_file *, struct vfsmount *, struct dentry *, char *);
> +int seq_dentry(struct seq_file *, struct dentry *, char *);
> 
>  int single_open(struct file *, int (*)(struct seq_file *, void *), void *);
>  int single_release(struct inode *, struct file *);

> This patch introduces a new proc interface that exposes all the propagation 
> trees within the namespace.
> 
> It walks through each off the mounts in the namespace, and prints the following information.
> 
> mount-id: a unique mount identifier
> dev-id : the unique device used to identify the device containing the filesystem
> path-from-root: mount point of the mount from /
> path-from-root-of-its-sb: path from its own root dentry.
> propagation-flag: SHARED, SLAVE, UNBINDABLE, PRIVATE
> peer-mount-id: the mount-id of its peer mount (if this mount is shared)
> master-mount-id: the mount-id of its master mount (if this mount is slave)
> 
> Using the above information one could easily write a script that can
> draw all the propagation trees in the namespace.
> 
> 
> Example:
> Here is a sample output of cat /proc/$$/mounts_propagation
> 
> 0xa917800 0x1 / / PRIVATE
> 0xa917200 0x6200 / / PRIVATE
> 0xa917180 0x3 /proc / PRIVATE
> 0xa917f80 0xa /dev/pts / PRIVATE
> 0xa917100 0x6210 /mnt / SHARED peer:0xa917100
> 0xa917f00 0x6210 /tmp /1 SLAVE master:0xa917100
> 0xa917900 0x6220 /mnt/2 / SHARED peer:0xa917900
> 
> line 5 indicates that the mount with id 0xa917100 is mounted at /mnt is shared
> and it is the only mount in its peer group.
> 
> line 6 indicates that the mount with id 0xa917f00 is mounted at /tmp, its 
> root is the dentry 1 present under its root directory. This mount is a
> slave mount and its master is the mount with id 0xa917100.
> 
> line 7 indicates that the mount with id 0xa917900 is mounted at /mnt/2, its 
> root is the dentry / of its filesystem. This mount is a
> shared and it is the only mount in its peer group.
> 
> one could write a script which runs through these lines and draws 4
> individual satellite mounts and two propagation trees, the first propagation
> tree has a shared mount and a slave mount.  and the second propagation tree has
> just one shared mount.
> 
> 	
> Signed-off-by: Ram Pai <linuxram@us.ibm.com>
> ---
>  fs/namespace.c |   42 ++++++++++++++++++++++++++++++++++++++++++
>  fs/pnode.c     |    6 ------
>  fs/pnode.h     |    6 ++++++
>  fs/proc/base.c |   22 +++++++++++++++++++++-
>  4 files changed, 69 insertions(+), 7 deletions(-)
> 
> Index: linux-2.6.17.10/fs/namespace.c
> ===================================================================
> --- linux-2.6.17.10.orig/fs/namespace.c
> +++ linux-2.6.17.10/fs/namespace.c
> @@ -410,6 +410,41 @@ static int show_vfsmnt_new(struct seq_fi
>  	return show_options(m, v);
>  }
> 
> +static int show_vfsmnt_propagation(struct seq_file *m, void *v)
> +{
> +	struct vfsmount *mnt = v;
> +	seq_printf(m, "0x%x", (int)mnt);
> +	seq_putc(m, ' ');
> +	seq_printf(m, "0x%x", new_encode_dev(mnt->mnt_sb->s_dev));
> +	seq_putc(m, ' ');
> +	seq_path(m, mnt, mnt->mnt_root, " \t\n\\");
> +	seq_putc(m, ' ');
> +	seq_dentry(m, mnt->mnt_root, " \t\n\\");
> +	seq_putc(m, ' ');
> +
> +	if (IS_MNT_SHARED(mnt)) {
> +		seq_printf(m, "%s ", "SHARED");
> +		if (IS_MNT_SLAVE(mnt)) {
> +			seq_printf(m, "%s ", "SLAVE");
> +		}
> +	} else if (IS_MNT_SLAVE(mnt)) {
> +		seq_printf(m, "%s ", "SLAVE");
> +	} else if (IS_MNT_UNBINDABLE(mnt)) {
> +		seq_printf(m, "%s ", "UNBINDABLE");
> +	} else {
> +		seq_printf(m, "%s ", "PRIVATE");
> +	}
> +
> +	if (IS_MNT_SHARED(mnt)) {
> +		seq_printf(m, "peer:0x%x ", (int)next_peer(mnt));

Ok, so if the sequence of events was

	mount --make-shared /mnt
	(some user logs in and gets a cloned namespace, so his /mnt
	becomes the next peer of /mnt)
	mount --bind /mnt /tmp
	(some other user logs in and gets cloned namespace...)

or some such sequence of events, we could lose all information
about /mnt and /tmp being peers, right?  Should a new
next_peer_in_same_namespace(mnt) be used rather than next_peer()?

Somewhat similarly,

> +	}
> +	if (IS_MNT_SLAVE(mnt)) {
> +		seq_printf(m, "master:0x%x ", (int)mnt->mnt_master);

Should we for privacy reasons not print out the address mnt->mnt_master
is in a different namespace (perhaps if !CAP_SYS_ADMIN)?

Otherwise I like this.

thanks,
-serge

> +	}
> +	seq_puts(m, "\n");
> +	return 0;
> +}
> +
>  struct seq_operations mounts_op = {
>  	.start	= m_start,
>  	.next	= m_next,
> @@ -424,6 +459,13 @@ struct seq_operations mounts_new_op = {
>  	.show	= show_vfsmnt_new
>  };
> 
> +struct seq_operations mounts_propagation_op = {
> +	.start	= m_start,
> +	.next	= m_next,
> +	.stop	= m_stop,
> +	.show	= show_vfsmnt_propagation
> +};
> +
>  static int show_vfsstat(struct seq_file *m, void *v)
>  {
>  	struct vfsmount *mnt = v;
> Index: linux-2.6.17.10/fs/proc/base.c
> ===================================================================
> --- linux-2.6.17.10.orig/fs/proc/base.c
> +++ linux-2.6.17.10/fs/proc/base.c
> @@ -105,6 +105,7 @@ enum pid_directory_inos {
>  	PROC_TGID_NUMA_MAPS,
>  	PROC_TGID_MOUNTS,
>  	PROC_TGID_MOUNTS_NEW,
> +	PROC_TGID_MOUNTS_PROPAGATION,
>  	PROC_TGID_MOUNTSTATS,
>  	PROC_TGID_WCHAN,
>  #ifdef CONFIG_MMU
> @@ -146,6 +147,7 @@ enum pid_directory_inos {
>  	PROC_TID_MAPS,
>  	PROC_TID_NUMA_MAPS,
>  	PROC_TID_MOUNTS,
> +	PROC_TID_MOUNTS_PROPAGATION,
>  	PROC_TID_MOUNTS_NEW,
>  	PROC_TID_MOUNTSTATS,
>  	PROC_TID_WCHAN,
> @@ -206,6 +208,7 @@ static struct pid_entry tgid_base_stuff[
>  	E(PROC_TGID_EXE,       "exe",     S_IFLNK|S_IRWXUGO),
>  	E(PROC_TGID_MOUNTS,    "mounts",  S_IFREG|S_IRUGO),
>  	E(PROC_TGID_MOUNTS_NEW,"mounts_new",  S_IFREG|S_IRUGO),
> +	E(PROC_TGID_MOUNTS_PROPAGATION,"mounts_propagation",  S_IFREG|S_IRUGO),
>  	E(PROC_TGID_MOUNTSTATS, "mountstats", S_IFREG|S_IRUSR),
>  #ifdef CONFIG_MMU
>  	E(PROC_TGID_SMAPS,     "smaps",   S_IFREG|S_IRUGO),
> @@ -250,6 +253,7 @@ static struct pid_entry tid_base_stuff[]
>  	E(PROC_TID_EXE,        "exe",     S_IFLNK|S_IRWXUGO),
>  	E(PROC_TID_MOUNTS,     "mounts",  S_IFREG|S_IRUGO),
>  	E(PROC_TID_MOUNTS_NEW, "mounts_new",  S_IFREG|S_IRUGO),
> +	E(PROC_TID_MOUNTS_PROPAGATION,"mounts_propagation",  S_IFREG|S_IRUGO),
>  #ifdef CONFIG_MMU
>  	E(PROC_TID_SMAPS,      "smaps",   S_IFREG|S_IRUGO),
>  #endif
> @@ -733,7 +737,7 @@ static int __mounts_open(struct inode *i
>  	return ret;
>  }
> 
> -extern struct seq_operations mounts_op, mounts_new_op;
> +extern struct seq_operations mounts_op, mounts_new_op, mounts_propagation_op;
>  static int mounts_open(struct inode *inode, struct file *file)
>  {
>  	return (__mounts_open(inode, file, &mounts_op));
> @@ -742,6 +746,10 @@ static int mounts_new_open(struct inode 
>  {
>  	return __mounts_open(inode, file, &mounts_new_op);
>  }
> +static int mounts_propagation_open(struct inode *inode, struct file *file)
> +{
> +	return __mounts_open(inode, file, &mounts_propagation_op);
> +}
> 
>  static int mounts_release(struct inode *inode, struct file *file)
>  {
> @@ -785,6 +793,14 @@ static struct file_operations proc_mount
>  	.poll		= mounts_poll,
>  };
> 
> +static struct file_operations proc_propagation_operations = {
> +	.open		= mounts_propagation_open,
> +	.read		= seq_read,
> +	.llseek		= seq_lseek,
> +	.release	= mounts_release,
> +	.poll		= mounts_poll,
> +};
> +
>  extern struct seq_operations mountstats_op;
>  static int mountstats_open(struct inode *inode, struct file *file)
>  {
> @@ -1825,6 +1841,10 @@ static struct dentry *proc_pident_lookup
>  		case PROC_TGID_MOUNTS_NEW:
>  			inode->i_fop = &proc_mounts_new_operations;
>  			break;
> +		case PROC_TID_MOUNTS_PROPAGATION:
> +		case PROC_TGID_MOUNTS_PROPAGATION:
> +			inode->i_fop = &proc_propagation_operations;
> +			break;
>  #ifdef CONFIG_MMU
>  		case PROC_TID_SMAPS:
>  		case PROC_TGID_SMAPS:
> Index: linux-2.6.17.10/fs/pnode.c
> ===================================================================
> --- linux-2.6.17.10.orig/fs/pnode.c
> +++ linux-2.6.17.10/fs/pnode.c
> @@ -11,12 +11,6 @@
>  #include <linux/fs.h>
>  #include "pnode.h"
> 
> -/* return the next shared peer mount of @p */
> -static inline struct vfsmount *next_peer(struct vfsmount *p)
> -{
> -	return list_entry(p->mnt_share.next, struct vfsmount, mnt_share);
> -}
> -
>  static inline struct vfsmount *first_slave(struct vfsmount *p)
>  {
>  	return list_entry(p->mnt_slave_list.next, struct vfsmount, mnt_slave);
> Index: linux-2.6.17.10/fs/pnode.h
> ===================================================================
> --- linux-2.6.17.10.orig/fs/pnode.h
> +++ linux-2.6.17.10/fs/pnode.h
> @@ -29,6 +29,12 @@ static inline void set_mnt_shared(struct
>  	mnt->mnt_flags |= MNT_SHARED;
>  }
> 
> +/* return the next shared peer mount of @p */
> +static inline struct vfsmount *next_peer(struct vfsmount *p)
> +{
> +	return list_entry(p->mnt_share.next, struct vfsmount, mnt_share);
> +}
> +
>  void change_mnt_propagation(struct vfsmount *, int);
>  int propagate_mnt(struct vfsmount *, struct dentry *, struct vfsmount *,
>  		struct list_head *);

Re: How to query mount propagation state?

[Ram Pai]

On Mon, 2007-04-16 at 14:16 -0500, Serge E. Hallyn wrote:
> > This patch introduces a new proc interface that exposes all the
> propagation 
> > trees within the namespace.
> > 
> > It walks through each off the mounts in the namespace, and prints
> the following information.
> > 
> > mount-id: a unique mount identifier
> > dev-id : the unique device used to identify the device containing
> the filesystem
> > path-from-root: mount point of the mount from /
> > path-from-root-of-its-sb: path from its own root dentry.
> > propagation-flag: SHARED, SLAVE, UNBINDABLE, PRIVATE
> > peer-mount-id: the mount-id of its peer mount (if this mount is
> shared)
> > master-mount-id: the mount-id of its master mount (if this mount is
> slave)
> > 
> > Using the above information one could easily write a script that can
> > draw all the propagation trees in the namespace.
> > 
> > 
> > Example:
> > Here is a sample output of cat /proc/$$/mounts_propagation
> > 
> > 0xa917800 0x1 / / PRIVATE
> > 0xa917200 0x6200 / / PRIVATE
> > 0xa917180 0x3 /proc / PRIVATE
> > 0xa917f80 0xa /dev/pts / PRIVATE
> > 0xa917100 0x6210 /mnt / SHARED peer:0xa917100
> > 0xa917f00 0x6210 /tmp /1 SLAVE master:0xa917100
> > 0xa917900 0x6220 /mnt/2 / SHARED peer:0xa917900
> > 
> > line 5 indicates that the mount with id 0xa917100 is mounted at /mnt
> is shared
> > and it is the only mount in its peer group.
> > 
> > line 6 indicates that the mount with id 0xa917f00 is mounted
> at /tmp, its 
> > root is the dentry 1 present under its root directory. This mount is
> a
> > slave mount and its master is the mount with id 0xa917100.
> > 
> > line 7 indicates that the mount with id 0xa917900 is mounted
> at /mnt/2, its 
> > root is the dentry / of its filesystem. This mount is a
> > shared and it is the only mount in its peer group.
> > 
> > one could write a script which runs through these lines and draws 4
> > individual satellite mounts and two propagation trees, the first
> propagation
> > tree has a shared mount and a slave mount.  and the second
> propagation tree has
> > just one shared mount.
> > 
> >       
> > Signed-off-by: Ram Pai <linuxram@us.ibm.com>
> > ---
> >  fs/namespace.c |   42 ++++++++++++++++++++++++++++++++++++++++++
> >  fs/pnode.c     |    6 ------
> >  fs/pnode.h     |    6 ++++++
> >  fs/proc/base.c |   22 +++++++++++++++++++++-
> >  4 files changed, 69 insertions(+), 7 deletions(-)
> > 
> > Index: linux-2.6.17.10/fs/namespace.c
> > ===================================================================
> > --- linux-2.6.17.10.orig/fs/namespace.c
> > +++ linux-2.6.17.10/fs/namespace.c
> > @@ -410,6 +410,41 @@ static int show_vfsmnt_new(struct seq_fi
> >       return show_options(m, v);
> >  }
> > 
> > +static int show_vfsmnt_propagation(struct seq_file *m, void *v)
> > +{
> > +     struct vfsmount *mnt = v;
> > +     seq_printf(m, "0x%x", (int)mnt);
> > +     seq_putc(m, ' ');
> > +     seq_printf(m, "0x%x", new_encode_dev(mnt->mnt_sb->s_dev));
> > +     seq_putc(m, ' ');
> > +     seq_path(m, mnt, mnt->mnt_root, " \t\n\\");
> > +     seq_putc(m, ' ');
> > +     seq_dentry(m, mnt->mnt_root, " \t\n\\");
> > +     seq_putc(m, ' ');
> > +
> > +     if (IS_MNT_SHARED(mnt)) {
> > +             seq_printf(m, "%s ", "SHARED");
> > +             if (IS_MNT_SLAVE(mnt)) {
> > +                     seq_printf(m, "%s ", "SLAVE");
> > +             }
> > +     } else if (IS_MNT_SLAVE(mnt)) {
> > +             seq_printf(m, "%s ", "SLAVE");
> > +     } else if (IS_MNT_UNBINDABLE(mnt)) {
> > +             seq_printf(m, "%s ", "UNBINDABLE");
> > +     } else {
> > +             seq_printf(m, "%s ", "PRIVATE");
> > +     }
> > +
> > +     if (IS_MNT_SHARED(mnt)) {
> > +             seq_printf(m, "peer:0x%x ", (int)next_peer(mnt));
> 
> Ok, so if the sequence of events was
> 
>         mount --make-shared /mnt
>         (some user logs in and gets a cloned namespace, so his /mnt
>         becomes the next peer of /mnt)
>         mount --bind /mnt /tmp
>         (some other user logs in and gets cloned namespace...)
> 
> or some such sequence of events, we could lose all information
> about /mnt and /tmp being peers, right?  Should a new
> next_peer_in_same_namespace(mnt) be used rather than next_peer()?

you are right. it should print next_peer(mnt) only if CAP_SYS_ADMIN,
else print next_peer_in_same_namespace(mnt).

> 
> Somewhat similarly,
> 
> > +     }
> > +     if (IS_MNT_SLAVE(mnt)) {
> > +             seq_printf(m, "master:0x%x ", (int)mnt->mnt_master);
> 
> Should we for privacy reasons not print out the address
> mnt->mnt_master
> is in a different namespace (perhaps if !CAP_SYS_ADMIN)?

right. it should print mnt->mnt_master if (CAP_SYS_ADMIN), otherwise
print master_in_same_namespace(mnt).

RP

> 
> Otherwise I like this.
> 
> thanks,
> -serge 

Re: How to query mount propagation state?

[Karel Zak]

On Mon, Apr 16, 2007 at 10:39:46AM -0700, Ram Pai wrote:

> This patch disambiguates multiple mount-instances of the same
> filesystem (or part of the same filesystem), by introducing a new
> interface /proc/mounts_new. The interface has the following format.
            ^^^^^^^^^^^^^^
 ... odd name. What will be the name for a next generation?
 "/proc/mounts_new_new"? :-)

> 'cat /proc/mounts' shows the following:
> /dev/root /mnt ext2 rw 0 0
> /dev/root /tmp1 ext2 rw 0 0
> 
> NOTE: The above mount entries, do not indicate that /tmp1 contains the same
> directory tree as /var/tmp.
> 
> But 'cat /proc/mounts_new' shows us the following:
> 0x6200 /mnt /var ext2 rw 0 0
> 0x6200 /tmp1 /var/tmp ext2 rw 0 0

 Can't you purely and simply add the fsid= option to /proc/mounts?

 /dev/root /mnt ext2 rw,fsid=0x6200 0 0 
 /dev/root /mnt ext2 rw,fsid=0x6200 0 0

 I think you can do it without a negative impact to userspace.

> This patch introduces a new proc interface that exposes all the propagation 
> trees within the namespace.

 Good idea.

> It walks through each off the mounts in the namespace, and prints the following information.
> 
> mount-id: a unique mount identifier
> dev-id : the unique device used to identify the device containing the filesystem
  ^^^^
 Why not major:minor?

> path-from-root: mount point of the mount from /
> path-from-root-of-its-sb: path from its own root dentry.
> propagation-flag: SHARED, SLAVE, UNBINDABLE, PRIVATE
> peer-mount-id: the mount-id of its peer mount (if this mount is shared)
> master-mount-id: the mount-id of its master mount (if this mount is slave)

> Example:
> Here is a sample output of cat /proc/$$/mounts_propagation
> 
> 0xa917800 0x1 / / PRIVATE
> 0xa917200 0x6200 / / PRIVATE
> 0xa917180 0x3 /proc / PRIVATE
> 0xa917f80 0xa /dev/pts / PRIVATE
> 0xa917100 0x6210 /mnt / SHARED peer:0xa917100
> 0xa917f00 0x6210 /tmp /1 SLAVE master:0xa917100
> 0xa917900 0x6220 /mnt/2 / SHARED peer:0xa917900

 Same thing (although the mounts_propagation makes more sense than
 mount_new from my point of view). 
 
 cat /proc/mounts (or /proc/$$/mounts)

 /dev/root /mnt ext2 rw,mid=0xa917100,did=0x6210,prop=SHARED,peer=0xa917100


 my $0.02...

    Karel

-- 
 Karel Zak  <kzak@redhat.com>

Re: How to query mount propagation state?

[Ram Pai]

On Mon, 2007-04-16 at 23:07 +0200, Karel Zak wrote:
> On Mon, Apr 16, 2007 at 10:39:46AM -0700, Ram Pai wrote:
> 
> > This patch disambiguates multiple mount-instances of the same
> > filesystem (or part of the same filesystem), by introducing a new
> > interface /proc/mounts_new. The interface has the following format.
>             ^^^^^^^^^^^^^^
>  ... odd name. What will be the name for a next generation?
>  "/proc/mounts_new_new"? :-)
> 

that was the name I came up with 6 months back :-). Yes It should be
something more appropriate. Maybe /proc/mounts_1 ? The next generation
one would be /proc/mounts_2 ? Suggestion?


> > 'cat /proc/mounts' shows the following:
> > /dev/root /mnt ext2 rw 0 0
> > /dev/root /tmp1 ext2 rw 0 0
> > 
> > NOTE: The above mount entries, do not indicate that /tmp1 contains the same
> > directory tree as /var/tmp.
> > 
> > But 'cat /proc/mounts_new' shows us the following:
> > 0x6200 /mnt /var ext2 rw 0 0
> > 0x6200 /tmp1 /var/tmp ext2 rw 0 0
> 
>  Can't you purely and simply add the fsid= option to /proc/mounts?
> 
>  /dev/root /mnt ext2 rw,fsid=0x6200 0 0 
>  /dev/root /mnt ext2 rw,fsid=0x6200 0 0
> 
>  I think you can do it without a negative impact to userspace.

ok. 

> 
> > This patch introduces a new proc interface that exposes all the propagation 
> > trees within the namespace.
> 
>  Good idea.
> 
> > It walks through each off the mounts in the namespace, and prints the following information.
> > 
> > mount-id: a unique mount identifier
> > dev-id : the unique device used to identify the device containing the filesystem
>   ^^^^
>  Why not major:minor?

	Thinking about it, I feel we dont need this field at all. Basically we
need a field that can be keyed-upon to find the corresponding record
in /proc/mounts_1. mount-id can be used as the matching field, provided
we add the mount-id field to /proc/mounts_1.
agree?

RP

> > path-from-root: mount point of the mount from /
> > path-from-root-of-its-sb: path from its own root dentry.
> > propagation-flag: SHARED, SLAVE, UNBINDABLE, PRIVATE
> > peer-mount-id: the mount-id of its peer mount (if this mount is shared)
> > master-mount-id: the mount-id of its master mount (if this mount is slave)
> 
> > Example:
> > Here is a sample output of cat /proc/$$/mounts_propagation
> > 
> > 0xa917800 0x1 / / PRIVATE
> > 0xa917200 0x6200 / / PRIVATE
> > 0xa917180 0x3 /proc / PRIVATE
> > 0xa917f80 0xa /dev/pts / PRIVATE
> > 0xa917100 0x6210 /mnt / SHARED peer:0xa917100
> > 0xa917f00 0x6210 /tmp /1 SLAVE master:0xa917100
> > 0xa917900 0x6220 /mnt/2 / SHARED peer:0xa917900
> 
>  Same thing (although the mounts_propagation makes more sense than
>  mount_new from my point of view). 
> 
>  cat /proc/mounts (or /proc/$$/mounts)
> 
>  /dev/root /mnt ext2 rw,mid=0xa917100,did=0x6210,prop=SHARED,peer=0xa917100
> 
> 
>  my $0.02...
> 
>     Karel
>