quoted text > Seems, most people would be happier with a new file, instead of
> extending /proc/mounts.
>
> This patch is the first attempt at doing that, as well as fixing the
> issues found in the previous submission.
>
> Thanks,
> Miklos
>
> ---
> From: Ram Pai <linuxram@us.ibm.com>
>
> /proc/mounts in its current state fail to disambiguate bind mounts, especially
> when the bind mount is subrooted. Also it does not capture propagation state of
> the mounts(shared-subtree). The following patch addresses the problem.
>
> The patch adds '/proc/<pid>/mountinfo' which contains a superset of
> the fields in '/proc/<pid>/mounts'. The following additional fields
> are added:
>
> mntid -- is a unique identifier of the mount
> parent -- the id of the parent mount
> major:minor -- value of st_dev for files on that filesystem
> dir -- the subdir in the filesystem which forms the root of this mount
> propagation-type in the form of <propagation_flag>[:<mntid>][,...]
> note: 'shared' flag is followed by the mntid of its peer mount
> 'slave' flag is followed by the mntid of its master mount
> 'private' flag stands by itself
> 'unbindable' flag stands by itself
>
> Also mount options are split into two fileds, the first containing the
> per mount flags, the second the per super block options.
>
> Here is a sample cat /proc/mounts after execution the following commands:
>
> mount --bind /mnt /mnt
> mount --make-shared /mnt
> mount --bind /mnt/1 /var
> mount --make-slave /var
> mount --make-shared /var
> mount --bind /var/abc /tmp
> mount --make-unbindable /proc
>
> 2 2 0:1 rootfs rootfs / / rw rw private
> 16 2 98:0 ext2 /dev/root / / rw rw private
> 17 16 0:3 proc /proc / /proc rw rw unbindable
> 18 16 0:10 devpts devpts /dev/pts / rw rw private
> 19 16 98:0 ext2 /dev/root /mnt /mnt rw rw shared:19
> 20 16 98:0 ext2 /dev/root /mnt/1 /var rw rw shared:21,slave:19
> 21 16 98:0 ext2 /dev/root /mnt/1/abc /tmp rw rw shared:20,slave:19
>
> For example, the last line indicates that:
>
> 1) The mount is a shared mount.
> 2) Its peer mount of mount with id 20
> 3) It is also a slave mount of the master-mount with the id 19
> 4) The filesystem on device with major/minor number 98:0 and subdirectory
> mnt/1/abc makes the root directory of this mount.
> 5) And finally the mount with id 16 is its parent.
>
>
> [mszeredi@suse.cz]:
>
> - new file, rearrange fields
> - for mount ID's use IDA (from the IDR library) instead of a 32bit
> counter, which could overflow
> - print canonical ID's (smallest one within the peer group) for peers
> and master, this is more useful, than a random ID within the same namespace
> - fix a couple of small bugs
> - remove inlines
> - style fixes
>
> Signed-off-by: Ram Pai <linuxram@us.ibm.com>
> Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
> ---
>
> Index: linux/fs/dcache.c
> ===================================================================
> --- linux.orig/fs/dcache.c 2008-01-18 19:21:38.000000000 +0100
> +++ linux/fs/dcache.c 2008-01-18 19:22:27.000000000 +0100
> @@ -1890,6 +1890,60 @@ char *dynamic_dname(struct dentry *dentr
> return memcpy(buffer, temp, sz);
> }
>
> +static int prepend(char **buffer, int *buflen, const char *str,
> + int namelen)
> +{
> + *buflen -= namelen;
> + if (*buflen < 0)
> + return 1;
> + *buffer -= namelen;
> + memcpy(*buffer, str, namelen);
> + return 0;
> +}
> +
> +/*
> + * Write full pathname from the root of the filesystem into the buffer.
> + */
> +char *dentry_path(struct dentry *dentry, char *buf, int buflen)
> +{
> + char *end = buf + buflen;
> + char *retval;
> +
> + spin_lock(&dcache_lock);
> + prepend(&end, &buflen, "__PLACEHOLDER__0_", 1);
> + if (!IS_ROOT(dentry) && d_unhashed(dentry)) {
> + if (prepend(&end, &buflen, "//deleted", 9))
> + goto Elong;
> + }
> + if (buflen < 1)
> + 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/fs/namespace.c
> ===================================================================
> --- linux.orig/fs/namespace.c 2008-01-18 19:21:38.000000000 +0100
> +++ linux/fs/namespace.c 2008-01-18 23:39:35.000000000 +0100
> @@ -27,6 +27,7 @@
> #include <linux/mount.h>
> #include <linux/ramfs.h>
> #include <linux/log2.h>
> +#include <linux/idr.h>
> #include <asm/uaccess.h>
> #include <asm/unistd.h>
> #include "pnode.h"
> @@ -39,6 +40,7 @@
> __cacheline_aligned_in_smp DEFINE_SPINLOCK(vfsmount_lock);
>
> static int event;
> +static DEFINE_IDA(mnt_id_ida);
>
> static struct list_head *mount_hashtable __read_mostly;
> static struct kmem_cache *mnt_cache __read_mostly;
> @@ -58,10 +60,41 @@ static inline unsigned long hash(struct
>
> #define MNT_WRITER_UNDERFLOW_LIMIT -(1<<16)
>
> +static int mnt_alloc_id(struct vfsmount *mnt)
> +{
> + int res;
> +
> + retry:
> + spin_lock(&vfsmount_lock);
> + res = ida_get_new(&mnt_id_ida, &mnt->mnt_id);
> + spin_unlock(&vfsmount_lock);
> + if (res == -EAGAIN) {
> + if (ida_pre_get(&mnt_id_ida, GFP_KERNEL))
> + goto retry;
> + res = -ENOMEM;
> + }
> + return res;
> +}
> +
> +static void mnt_free_id(struct vfsmount *mnt)
> +{
> + spin_lock(&vfsmount_lock);
> + ida_remove(&mnt_id_ida, mnt->mnt_id);
> + spin_unlock(&vfsmount_lock);
> +}
> +
> struct vfsmount *alloc_vfsmnt(const char *name)
> {
> struct vfsmount *mnt = kmem_cache_zalloc(mnt_cache, GFP_KERNEL);
> if (mnt) {
> + int err;
> +
> + err = mnt_alloc_id(mnt);
> + if (err) {
> + kmem_cache_free(mnt_cache, mnt);
> + return NULL;
> + }
> +
> atomic_set(&mnt->mnt_count, 1);
> INIT_LIST_HEAD(&mnt->mnt_hash);
> INIT_LIST_HEAD(&mnt->mnt_child);
> @@ -338,6 +371,7 @@ EXPORT_SYMBOL(simple_set_mnt);
> void free_vfsmnt(struct vfsmount *mnt)
> {
> kfree(mnt->mnt_devname);
> + mnt_free_id(mnt);
> kmem_cache_free(mnt_cache, mnt);
> }
>
> @@ -601,28 +635,29 @@ static inline void mangle(struct seq_fil
> seq_escape(m, s, " \t\n\");
> }
>
> +static struct proc_fs_info {
> + int flag;
> + char *str;
> +} fs_info[] = {
> + { MS_SYNCHRONOUS, ",sync" },
> + { MS_DIRSYNC, ",dirsync" },
> + { MS_MANDLOCK, ",mand" },
> + { 0, NULL }
> +};
> +static struct proc_fs_info mnt_info[] = {
> + { MNT_NOSUID, ",nosuid" },
> + { MNT_NODEV, ",nodev" },
> + { MNT_NOEXEC, ",noexec" },
> + { MNT_NOATIME, ",noatime" },
> + { MNT_NODIRATIME, ",nodiratime" },
> + { MNT_RELATIME, ",relatime" },
> + { 0, NULL }
> +};
> +
> static int show_vfsmnt(struct seq_file *m, void *v)
> {
> struct vfsmount *mnt = list_entry(v, struct vfsmount, mnt_list);
> int err = 0;
> - static struct proc_fs_info {
> - int flag;
> - char *str;
> - } fs_info[] = {
> - { MS_SYNCHRONOUS, ",sync" },
> - { MS_DIRSYNC, ",dirsync" },
> - { MS_MANDLOCK, ",mand" },
> - { 0, NULL }
> - };
> - static struct proc_fs_info mnt_info[] = {
> - { MNT_NOSUID, ",nosuid" },
> - { MNT_NODEV, ",nodev" },
> - { MNT_NOEXEC, ",noexec" },
> - { MNT_NOATIME, ",noatime" },
> - { MNT_NODIRATIME, ",nodiratime" },
> - { MNT_RELATIME, ",relatime" },
> - { 0, NULL }
> - };
> struct proc_fs_info *fs_infop;
> struct path mnt_path = { .dentry = mnt->mnt_root, .mnt = mnt };
>
> @@ -657,6 +692,63 @@ struct seq_operations mounts_op = {
> .show = show_vfsmnt
> };
>
> +static int show_mountinfo(struct seq_file *m, void *v)
> +{
> + struct vfsmount *mnt = list_entry(v, struct vfsmount, mnt_list);
> + struct super_block *sb = mnt->mnt_sb;
> + struct path mnt_path = { .dentry = mnt->mnt_root, .mnt = mnt };
> + struct proc_fs_info *fs_infop;
> + int err = 0;
> +
> + seq_printf(m, "%i %i %u:%u ", mnt->mnt_id, mnt->mnt_parent->mnt_id,
> + MAJOR(sb->s_dev), MINOR(sb->s_dev));
> + mangle(m, sb->s_type->name);
> + if (sb->s_subtype && sb->s_subtype[0]) {
> + seq_putc(m, '.');
> + mangle(m, sb->s_subtype);
> + }
> + seq_putc(m, ' ');
> + mangle(m, mnt->mnt_devname ? mnt->mnt_devname : "none");
> + seq_putc(m, ' ');
> + seq_dentry(m, mnt->mnt_root, " \t\n\");
> + seq_putc(m, ' ');
> + seq_path(m, &mnt_path, " \t\n\");
> + seq_putc(m, ' ');
> + seq_puts(m, mnt->mnt_flags & MNT_READONLY ? "ro" : "rw");
> + for (fs_infop = mnt_info; fs_infop->flag; fs_infop++) {
> + if (mnt->mnt_flags & fs_infop->flag)
> + seq_puts(m, fs_infop->str);
> + }
> + seq_putc(m, ' ');
> + seq_puts(m, sb->s_flags & MS_RDONLY ? "ro" : "rw");
> + for (fs_infop = fs_info; fs_infop->flag; fs_infop++) {
> + if (sb->s_flags & fs_infop->flag)
> + seq_puts(m, fs_infop->str);
> + }
> + if (sb->s_op->show_options)
> + err = sb->s_op->show_options(m, mnt);
> + if (IS_MNT_SHARED(mnt)) {
> + seq_printf(m, " shared:%i", get_peer_group_id(mnt));
> + if (IS_MNT_SLAVE(mnt))
> + seq_printf(m, ",slave:%i", get_master_id(mnt));
> + } else if (IS_MNT_SLAVE(mnt)) {
> + seq_printf(m, " slave:%i", get_master_id(mnt));
> + } else if (IS_MNT_UNBINDABLE(mnt)) {
> + seq_printf(m, " unbindable");
> + } else {
> + seq_printf(m, " private");
> + }
> + seq_putc(m, '\n');
> + return err;
> +}
> +
> +struct seq_operations mountinfo_op = {
> + .start = m_start,
> + .next = m_next,
> + .stop = m_stop,
> + .show = show_mountinfo,
> +};
> +
> static int show_vfsstat(struct seq_file *m, void *v)
> {
> struct vfsmount *mnt = list_entry(v, struct vfsmount, mnt_list);
> Index: linux/fs/seq_file.c
> ===================================================================
> --- linux.orig/fs/seq_file.c 2008-01-18 19:21:38.000000000 +0100
> +++ linux/fs/seq_file.c 2008-01-18 19:22:27.000000000 +0100
> @@ -349,28 +349,40 @@ int seq_printf(struct seq_file *m, const
> }
> EXPORT_SYMBOL(seq_printf);
>
> +static 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 path *path, char *esc)
> {
> if (m->count < m->size) {
> char *s = m->buf + m->count;
> char *p = d_path(path, 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;
> }
> }
> }
> @@ -379,6 +391,28 @@ int seq_path(struct seq_file *m, struct
> }
> 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)
> +{
> + if (m->count < m->size) {
> + char *s = m->buf + m->count;
> + char *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 -1;
> +}
> +EXPORT_SYMBOL(seq_dentry);
> +
> static void *single_start(struct seq_file *p, loff_t *pos)
> {
> return NULL + (*pos == 0);
> Index: linux/include/linux/dcache.h
> ===================================================================
> --- linux.orig/include/linux/dcache.h 2008-01-18 19:21:38.000000000 +0100
> +++ linux/include/linux/dcache.h 2008-01-18 19:22:27.000000000 +0100
> @@ -302,6 +302,7 @@ extern int d_validate(struct dentry *, s
> extern char *dynamic_dname(struct dentry *, char *, int, const char *, ...);
>
> extern char *d_path(struct path *, char *, int);
> +extern char *dentry_path(struct dentry *, char *, int);
>
> /* Allocation counts.. */
>
> Index: linux/include/linux/seq_file.h
> ===================================================================
> --- linux.orig/include/linux/seq_file.h 2008-01-18 19:21:38.000000000 +0100
> +++ linux/include/linux/seq_file.h 2008-01-18 19:22:27.000000000 +0100
> @@ -10,6 +10,7 @@ struct seq_operations;
> struct file;
> struct path;
> struct inode;
> +struct dentry;
>
> struct seq_file {
> char *buf;
> @@ -43,6 +44,7 @@ int seq_printf(struct seq_file *, const
> __attribute__ ((format (printf,2,3)));
>
> int seq_path(struct seq_file *, struct path *, 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 *);
> Index: linux/fs/pnode.c
> ===================================================================
> --- linux.orig/fs/pnode.c 2008-01-18 19:21:38.000000000 +0100
> +++ linux/fs/pnode.c 2008-01-18 19:22:27.000000000 +0100
> @@ -27,6 +27,41 @@ static inline struct vfsmount *next_slav
> return list_entry(p->mnt_slave.next, struct vfsmount, mnt_slave);
> }
>
> +static int __peer_group_id(struct vfsmount *mnt)
> +{
> + struct vfsmount *m;
> + int id = mnt->mnt_id;
> +
> + for (m = next_peer(mnt); m != mnt; m = next_peer(m))
> + id = min(id, m->mnt_id);
> +
> + return id;
> +}
> +
> +/* return the smallest ID within the peer group */
> +int get_peer_group_id(struct vfsmount *mnt)
> +{
> + int id;
> +
> + spin_lock(&vfsmount_lock);
> + id = __peer_group_id(mnt);
> + spin_unlock(&vfsmount_lock);
> +
> + return id;
> +}
> +
> +/* return the smallest ID within the master's peer group */
> +int get_master_id(struct vfsmount *mnt)
> +{
> + int id;
> +
> + spin_lock(&vfsmount_lock);
> + id = __peer_group_id(mnt->mnt_master);
> + spin_unlock(&vfsmount_lock);
> +
> + return id;
> +}
> +
> static int do_make_slave(struct vfsmount *mnt)
> {
> struct vfsmount *peer_mnt = mnt, *master = mnt->mnt_master;
> Index: linux/fs/pnode.h
> ===================================================================
> --- linux.orig/fs/pnode.h 2008-01-18 19:21:38.000000000 +0100
> +++ linux/fs/pnode.h 2008-01-18 23:39:35.000000000 +0100
> @@ -35,4 +35,6 @@ int propagate_mnt(struct vfsmount *, str
> struct list_head *);
> int propagate_umount(struct list_head *);
> int propagate_mount_busy(struct vfsmount *, int);
> +int get_peer_group_id(struct vfsmount *);
> +int get_master_id(struct vfsmount *);
> #endif /* _LINUX_PNODE_H */
> Index: linux/include/linux/mount.h
> ===================================================================
> --- linux.orig/include/linux/mount.h 2008-01-18 19:21:38.000000000 +0100
> +++ linux/include/linux/mount.h 2008-01-18 23:39:35.000000000 +0100
> @@ -56,6 +56,7 @@ struct vfsmount {
> struct list_head mnt_slave; /* slave list entry */
> struct vfsmount *mnt_master; /* slave is on master->mnt_slave_list */
> struct mnt_namespace *mnt_ns; /* containing namespace */
> + int mnt_id; /* mount identifier */
> /*
> * We put mnt_count & mnt_expiry_mark at the end of struct vfsmount
> * to let these frequently modified fields in a separate cache line
> Index: linux/fs/proc/base.c
> ===================================================================
> --- linux.orig/fs/proc/base.c 2008-01-18 19:21:38.000000000 +0100
> +++ linux/fs/proc/base.c 2008-01-18 19:22:27.000000000 +0100
> @@ -435,13 +435,13 @@ static const struct inode_operations pro
> .setattr = proc_setattr,
> };
>
> -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_common(struct inode *inode, struct file *file,
> + struct seq_operations *op)
> {
> struct task_struct *task = get_proc_task(inode);
> struct nsproxy *nsp;
> @@ -467,7 +467,7 @@ 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, op);
> if (!ret) {
> p->m.private = ns;
> p->event = ns->event;
> @@ -506,6 +506,11 @@ static unsigned mounts_poll(struct file
> return res;
> }
>
> +static int mounts_open(struct inode *inode, struct file *file)
> +{
> + return mounts_open_common(inode, file, &mounts_op);
> +}
> +
> static const struct file_operations proc_mounts_operations = {
> .open = mounts_open,
> .read = seq_read,
> @@ -514,38 +519,22 @@ static const struct file_operations proc
> .poll = mounts_poll,
> };
>
> -extern struct seq_operations mountstats_op;
> -static int mountstats_open(struct inode *inode, struct file *file)
> +static int mountinfo_open(struct inode *inode, struct file *file)
> {
> - int ret = seq_open(file, &mountstats_op);
> -
> - if (!ret) {
> - struct seq_file *m = file->private_data;
> - struct nsproxy *nsp;
> - struct mnt_namespace *mnt_ns = NULL;
> - struct task_struct *task = get_proc_task(inode);
> -
> - if (task) {
> - rcu_read_lock();
> - nsp = task_nsproxy(task);
> - if (nsp) {
> - mnt_ns = nsp->mnt_ns;
> - if (mnt_ns)
> - get_mnt_ns(mnt_ns);
> - }
> - rcu_read_unlock();
> + return mounts_open_common(inode, file, &mountinfo_op);
> +}
>
> - put_task_struct(task);
> - }
> +static const struct file_operations proc_mountinfo_operations = {
> + .open = mountinfo_open,
> + .read = seq_read,
> + .llseek = seq_lseek,
> + .release = mounts_release,
> + .poll = mounts_poll,
> +};
>
> - if (mnt_ns)
> - m->private = mnt_ns;
> - else {
> - seq_release(inode, file);
> - ret = -EINVAL;
> - }
> - }
> - return ret;
> +static int mountstats_open(struct inode *inode, struct file *file)
> +{
> + return mounts_open_common(inode, file, &mountstats_op);
> }
>
> static const struct file_operations proc_mountstats_operations = {
> @@ -2220,6 +2209,7 @@ static const struct pid_entry tgid_base_
> LNK("root", root),
> LNK("exe", exe),
> REG("mounts", S_IRUGO, mounts),
> + REG("mountinfo", S_IRUGO, mountinfo),
> REG("mountstats", S_IRUSR, mountstats),
> #ifdef CONFIG_PROC_PAGE_MONITOR
> REG("clear_refs", S_IWUSR, clear_refs),
> @@ -2548,6 +2538,7 @@ static const struct pid_entry tid_base_s
> LNK("root", root),
> LNK("exe", exe),
> REG("mounts", S_IRUGO, mounts),
> + REG("mountinfo", S_IRUGO, mountinfo),
> #ifdef CONFIG_PROC_PAGE_MONITOR
> REG("clear_refs", S_IWUSR, clear_refs),
> REG("smaps", S_IRUGO, smaps),
> Index: linux/include/linux/mnt_namespace.h
> ===================================================================
> --- linux.orig/include/linux/mnt_namespace.h 2008-01-18 19:21:38.000000000 +0100
> +++ linux/include/linux/mnt_namespace.h 2008-01-18 19:22:27.000000000 +0100
> @@ -37,5 +37,9 @@ static inline void get_mnt_ns(struct mnt
> atomic_inc(&ns->count);
> }
>
> +extern struct seq_operations mounts_op;
> +extern struct seq_operations mountinfo_op;
> +extern struct seq_operations mountstats_op;
> +
> #endif
> #endif
> Index: linux/fs/proc/proc_misc.c
> ===================================================================
> --- linux.orig/fs/proc/proc_misc.c 2008-01-18 19:21:38.000000000 +0100
> +++ linux/fs/proc/proc_misc.c 2008-01-19 11:56:33.000000000 +0100
> @@ -980,6 +980,7 @@ 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("mountinfo", NULL, "self/mountinfo");
>
> /* And now for trickier ones */
> #ifdef CONFIG_PRINTK
-
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