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    Subject[PATCH] [NET] dont insert socket dentries into dentry_hashtable.
    Date
    We currently insert socket dentries into the global dentry hashtable.
    This is *suboptimal* because there is currently no way these entries can be
    used for a lookup(). (/proc/xxx/fd/xxx uses a different mechanism). Inserting
    them in dentry hashtable slow dcache lookups.


    To let __dpath() still work correctly (ie not adding a " (deleted)") after
    dentry name, we do :

    - Right after d_alloc(), pretend they are hashed by clearing the
    DCACHE_UNHASHED bit.

    - Call d_instantiate() instead of d_add() : dentry is not inserted in hash
    table.

    __dpath() & friends work as intended during dentry lifetime.

    - At dismantle time, once dput() must clear the dentry, setting again
    DCACHE_UNHASHED bit inside the custom d_delete() function provided by socket
    code, so that dput() can just kill_it.

    Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
    --- linux-2.6.19-rc6/net/socket.c 2006-11-22 17:33:41.000000000 +0100
    +++ linux-2.6.19-rc6-ed/net/socket.c 2006-11-22 18:28:12.000000000 +0100
    @@ -306,7 +306,14 @@ static struct file_system_type sock_fs_t

    static int sockfs_delete_dentry(struct dentry *dentry)
    {
    - return 1;
    + /*
    + * At creation time, we pretended this dentry was hashed
    + * (by clearing DCACHE_UNHASHED bit in d_flags)
    + * At delete time, we restore the truth : not hashed.
    + * (so that dput() can proceed correctly)
    + */
    + dentry->d_flags |= DCACHE_UNHASHED;
    + return 0;
    }
    static struct dentry_operations sockfs_dentry_operations = {
    .d_delete = sockfs_delete_dentry,
    @@ -354,14 +361,20 @@ static int sock_attach_fd(struct socket

    this.len = sprintf(name, "[%lu]", SOCK_INODE(sock)->i_ino);
    this.name = name;
    - this.hash = SOCK_INODE(sock)->i_ino;
    + this.hash = 0;

    file->f_dentry = d_alloc(sock_mnt->mnt_sb->s_root, &this);
    if (unlikely(!file->f_dentry))
    return -ENOMEM;

    file->f_dentry->d_op = &sockfs_dentry_operations;
    - d_add(file->f_dentry, SOCK_INODE(sock));
    + /*
    + * We dont want to push this dentry into global dentry hash table.
    + * We pretend dentry is already hashed, by unsetting DCACHE_UNHASHED
    + * This permits a working /proc/$pid/fd/XXX on sockets
    + */
    + file->f_dentry->d_flags &= ~DCACHE_UNHASHED;
    + d_instantiate(file->f_dentry, SOCK_INODE(sock));
    file->f_vfsmnt = mntget(sock_mnt);
    file->f_mapping = file->f_dentry->d_inode->i_mapping;
    \
     
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      Last update: 2006-11-22 19:03    [W:0.022 / U:30.368 seconds]
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