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    Subject[RFC 1/6] sysfs backing store v0.3


    = changes in version 0.3
    o Nil, just re-diffed

    => changes in version 0.2
    o Nil, just re-diffed

    => changes in version 0.1
    o Corrected sysfs_umount_begin(), it doesnot need lock_super() and also the
    s_root check is not required. The reason being, that sysfs filesystem is
    always mounted internally during init and there is no chance of sysfs super
    block going away.

    o corrected comments for umount_begin()

    ============================================================================
    o The following patch contains the sysfs_dirent structure definition.
    sysfs_dirent can represent kobject, attribute group, text attribute or
    binary attribute for kobjects registered with sysfs. sysfs_dirent is
    allocated with a ref count (s_count) of 1. Ref count is incremented when
    a dentry is associated with the sysfs_dirent and it is decremented when
    the corresponding dentry is freed.

    o sysfs_dirent's corresponding to the attribute files of a kobject or attribute
    group are linked together with s_sibling and are anchored at s_children of
    the corresponding kobject's or attribute-group's sysfs_dirent.

    o The patch also contains the mount related changes for sysfs backing store.
    Because we mount sysfs once while init(), plain umount of sysfs doesnot
    free all the un-used dentries (present in LRU list). To use force umount
    flag, umount_begin() routine is provided which does a shrink_dcache_parent()
    to release all the unused dentries.



    fs/sysfs/mount.c | 27 +++++++++++++++++++++++++--
    include/linux/sysfs.h | 19 +++++++++++++++++++
    2 files changed, 44 insertions(+), 2 deletions(-)

    diff -puN fs/sysfs/mount.c~sysfs-leaves-mount fs/sysfs/mount.c
    --- linux-2.6.5-rc1/fs/sysfs/mount.c~sysfs-leaves-mount 2004-03-18 11:35:22.000000000 +0530
    +++ linux-2.6.5-rc1-maneesh/fs/sysfs/mount.c 2004-03-18 11:35:22.000000000 +0530
    @@ -20,6 +20,14 @@ struct super_block * sysfs_sb = NULL;
    static struct super_operations sysfs_ops = {
    .statfs = simple_statfs,
    .drop_inode = generic_delete_inode,
    + .umount_begin = sysfs_umount_begin,
    +};
    +
    +struct sysfs_dirent sysfs_root = {
    + .s_sibling = LIST_HEAD_INIT(sysfs_root.s_sibling),
    + .s_children = LIST_HEAD_INIT(sysfs_root.s_children),
    + .s_element = NULL,
    + .s_type = SYSFS_ROOT,
    };

    static int sysfs_fill_super(struct super_block *sb, void *data, int silent)
    @@ -35,8 +43,8 @@ static int sysfs_fill_super(struct super

    inode = sysfs_new_inode(S_IFDIR | S_IRWXU | S_IRUGO | S_IXUGO);
    if (inode) {
    - inode->i_op = &simple_dir_inode_operations;
    - inode->i_fop = &simple_dir_operations;
    + inode->i_op = &sysfs_dir_inode_operations;
    + inode->i_fop = &sysfs_dir_operations;
    /* directory inodes start off with i_nlink == 2 (for "." entry) */
    inode->i_nlink++;
    } else {
    @@ -50,6 +58,7 @@ static int sysfs_fill_super(struct super
    iput(inode);
    return -ENOMEM;
    }
    + root->d_fsdata = &sysfs_root;
    sb->s_root = root;
    return 0;
    }
    @@ -60,6 +69,20 @@ static struct super_block *sysfs_get_sb(
    return get_sb_single(fs_type, flags, data, sysfs_fill_super);
    }

    +/* For freeing zero refenced dentries / inodes while force unmounting
    + *
    + * sysfs is mounted once within kernel during init(), and this keeps the super
    + * block always active. So in case of user just doing normal umount,
    + * ->kill_sb is never called. So, in order to immediately free the memory used
    + * by un-used dentries and inodes, sysfs should to be umounted with force
    + * option. In anycase there will be normal pruing of unused dentries/inodes
    + * as usual due to memory pressure.
    + */
    +void sysfs_umount_begin(struct super_block * sb)
    +{
    + shrink_dcache_parent(sb->s_root);
    +}
    +
    static struct file_system_type sysfs_fs_type = {
    .name = "sysfs",
    .get_sb = sysfs_get_sb,
    diff -puN include/linux/sysfs.h~sysfs-leaves-mount include/linux/sysfs.h
    --- linux-2.6.5-rc1/include/linux/sysfs.h~sysfs-leaves-mount 2004-03-18 11:35:22.000000000 +0530
    +++ linux-2.6.5-rc1-maneesh/include/linux/sysfs.h 2004-03-18 11:35:22.000000000 +0530
    @@ -9,6 +9,8 @@
    #ifndef _SYSFS_H_
    #define _SYSFS_H_

    +#include <asm/atomic.h>
    +
    struct kobject;
    struct module;

    @@ -42,6 +44,23 @@ sysfs_remove_dir(struct kobject *);
    extern void
    sysfs_rename_dir(struct kobject *, const char *new_name);

    +struct sysfs_dirent {
    + atomic_t s_count;
    + struct list_head s_sibling;
    + struct list_head s_children;
    + void * s_element;
    + int s_type;
    + struct dentry * s_dentry;
    +};
    +
    +#define SYSFS_ROOT 0x0001
    +#define SYSFS_KOBJECT 0x0002
    +#define SYSFS_KOBJ_ATTR 0x0004
    +#define SYSFS_KOBJ_BIN_ATTR 0x0008
    +#define SYSFS_KOBJ_ATTR_GROUP 0x0010
    +#define SYSFS_KOBJ_LINK 0x0020
    +#define SYSFS_NOT_PINNED (SYSFS_KOBJ_ATTR | SYSFS_KOBJ_BIN_ATTR | SYSFS_KOBJ_LINK)
    +
    extern int
    sysfs_create_file(struct kobject *, const struct attribute *);

    _
    --
    Maneesh Soni
    Linux Technology Center,
    IBM Software Lab, Bangalore, India
    email: maneesh@in.ibm.com
    Phone: 91-80-25044999 Fax: 91-80-25268553
    T/L : 9243696
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