From 304e61e6fbadec586dfe002b535f169a04248e49 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Wed, 6 Dec 2006 20:38:49 -0800 Subject: [PATCH] [PATCH] net: don't insert socket dentries into dentry_hashtable 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 slows 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 Cc: Al Viro Acked-by: "David S. Miller" Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- net/socket.c | 19 ++++++++++++++++--- 1 file changed, 16 insertions(+), 3 deletions(-) diff --git a/net/socket.c b/net/socket.c index 43eff489c8..29ea1de43e 100644 --- a/net/socket.c +++ b/net/socket.c @@ -305,7 +305,14 @@ static struct file_system_type sock_fs_type = { 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, @@ -353,14 +360,20 @@ static int sock_attach_fd(struct socket *sock, struct file *file) 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; -- 2.39.5