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    Subject[PATCH] Make sysctl a separate filesystem
    Sysctl files/inodes now have their own readdir and lookup
    methods, so there is one step left in turning this into a
    separate filesystem.

    The benefits of this are:

    1. this will allow to remove a fancy revalidation rules from
    sysctl dentries (will be in a separate patch);
    2. the same approach will make /proc/net implementation MUCH
    cleaner in respect to net namespaces interaction, i.e.
    no racy shadows and no revalidation for proc entries in
    this subdir;
    3. sysctl inodes are now smaller than the procfs ones.

    Note: update your initscripts to mount sysctl filesystem
    right after the proc is mounted in order not to lose your
    /etc/sysctl.conf configuration (and optionally fstab).

    Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
    Signed-off-by: Alexey Dobriyan <adobriyan@openvz.org>

    ---

    diff --git a/fs/proc/internal.h b/fs/proc/internal.h
    index 1c81c8f..47dec4b 100644
    --- a/fs/proc/internal.h
    +++ b/fs/proc/internal.h
    @@ -11,11 +11,6 @@

    #include <linux/proc_fs.h>

    -#ifdef CONFIG_PROC_SYSCTL
    -extern int proc_sys_init(void);
    -#else
    -static inline void proc_sys_init(void) { }
    -#endif
    #ifdef CONFIG_NET
    extern int proc_net_init(void);
    #else
    diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
    index 614c34b..1b52f43 100644
    --- a/fs/proc/proc_sysctl.c
    +++ b/fs/proc/proc_sysctl.c
    @@ -1,11 +1,9 @@
    /*
    * /proc/sys support
    */
    -
    +#include <linux/magic.h>
    #include <linux/sysctl.h>
    -#include <linux/proc_fs.h>
    #include <linux/security.h>
    -#include "internal.h"

    static struct dentry_operations proc_sys_dentry_operations;
    static const struct file_operations proc_sys_file_operations;
    @@ -28,22 +26,26 @@ static void proc_sys_refresh_inode(struct inode *inode, struct ctl_table *table)
    }
    }

    +static inline long inode_depth(struct inode *ino)
    +{
    + return (long)ino->i_private;
    +}
    +
    +static inline void set_inode_depth(struct inode *ino, long depth)
    +{
    + ino->i_private = (void *)depth;
    +}
    +
    static struct inode *proc_sys_make_inode(struct inode *dir, struct ctl_table *table)
    {
    struct inode *inode;
    - struct proc_inode *dir_ei, *ei;
    - int depth;

    inode = new_inode(dir->i_sb);
    if (!inode)
    goto out;

    /* A directory is always one deeper than it's parent */
    - dir_ei = PROC_I(dir);
    - depth = dir_ei->fd + 1;
    -
    - ei = PROC_I(inode);
    - ei->fd = depth;
    + set_inode_depth(inode, inode_depth(dir) + 1);
    inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
    inode->i_op = &proc_sys_inode_operations;
    inode->i_fop = &proc_sys_file_operations;
    @@ -56,10 +58,7 @@ out:
    static struct dentry *proc_sys_ancestor(struct dentry *dentry, int depth)
    {
    for (;;) {
    - struct proc_inode *ei;
    -
    - ei = PROC_I(dentry->d_inode);
    - if (ei->fd == depth)
    + if (inode_depth(dentry->d_inode) == depth)
    break; /* found */

    dentry = dentry->d_parent;
    @@ -93,12 +92,9 @@ static struct ctl_table *proc_sys_lookup_table(struct dentry *dentry,
    struct ctl_table *table)
    {
    struct dentry *ancestor;
    - struct proc_inode *ei;
    int depth, i;

    - ei = PROC_I(dentry->d_inode);
    - depth = ei->fd;
    -
    + depth = inode_depth(dentry->d_inode);
    if (depth == 0)
    return table;

    @@ -385,7 +381,7 @@ static int proc_sys_permission(struct inode *inode, int mask, struct nameidata *
    int error;

    head = NULL;
    - depth = PROC_I(inode)->fd;
    + depth = inode_depth(inode);

    /* First check the cached permissions, in case we don't have
    * enough information to lookup the sysctl table entry.
    @@ -466,13 +462,56 @@ static struct dentry_operations proc_sys_dentry_operations = {
    .d_revalidate = proc_sys_revalidate,
    };

    -static struct proc_dir_entry *proc_sys_root;
    +static const struct super_operations sysctl_ops = {
    + .statfs = simple_statfs,
    + .drop_inode = generic_delete_inode,
    +};

    -int proc_sys_init(void)
    +static int sysctl_fill_super(struct super_block *sb, void *data, int flags)
    {
    - proc_sys_root = proc_mkdir("sys", NULL);
    - proc_sys_root->proc_iops = &proc_sys_inode_operations;
    - proc_sys_root->proc_fops = &proc_sys_file_operations;
    - proc_sys_root->nlink = 0;
    + struct inode *ino;
    +
    + sb->s_flags |= MS_NODIRATIME | MS_NOSUID | MS_NOEXEC | MS_NODEV;
    + sb->s_blocksize = 1024;
    + sb->s_blocksize_bits = 10;
    + sb->s_magic = PROC_SUPER_MAGIC;
    + sb->s_op = &sysctl_ops;
    + sb->s_time_gran = 1;
    +
    + ino = new_inode(sb);
    + if (ino == NULL)
    + return -ENOMEM;
    +
    + ino->i_op = &proc_sys_inode_operations;
    + ino->i_fop = &proc_sys_file_operations;
    + set_inode_depth(ino, 0);
    + ino->i_uid = 0;
    + ino->i_gid = 0;
    + ino->i_mode = 0555 | S_IFDIR;
    +
    + sb->s_root = d_alloc_root(ino);
    + if (sb->s_root == NULL) {
    + iput(ino);
    + return -ENOMEM;
    + }
    +
    return 0;
    }
    +
    +static int sysctl_get_sb(struct file_system_type *fs_type,
    + int flags, const char *dev_name, void *data, struct vfsmount *mnt)
    +{
    + return get_sb_single(fs_type, flags, data, sysctl_fill_super, mnt);
    +}
    +
    +static struct file_system_type sysctl_fs = {
    + .name = "sysctl",
    + .get_sb = sysctl_get_sb,
    + .kill_sb = kill_anon_super,
    +};
    +
    +static int __init proc_sys_init(void)
    +{
    + return register_filesystem(&sysctl_fs);
    +}
    +module_init(proc_sys_init);
    diff --git a/fs/proc/root.c b/fs/proc/root.c
    index ef0fb57..9035938 100644
    --- a/fs/proc/root.c
    +++ b/fs/proc/root.c
    @@ -129,6 +129,7 @@ void __init proc_root_init(void)
    proc_root_fs = proc_mkdir("fs", NULL);
    proc_root_driver = proc_mkdir("driver", NULL);
    proc_mkdir("fs/nfsd", NULL); /* somewhere for the nfsd filesystem to be mounted */
    + proc_mkdir("sys", NULL);
    #if defined(CONFIG_SUN_OPENPROMFS) || defined(CONFIG_SUN_OPENPROMFS_MODULE)
    /* just give it a mountpoint */
    proc_mkdir("openprom", NULL);
    @@ -138,7 +139,6 @@ void __init proc_root_init(void)
    proc_device_tree_init();
    #endif
    proc_bus = proc_mkdir("bus", NULL);
    - proc_sys_init();
    }

    static int proc_root_getattr(struct vfsmount *mnt, struct dentry *dentry, struct kstat *stat


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