[PATCH] net: don't insert socket dentries into dentry_hashtable (304e61e6) · Commits · 戴 / test

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 <dada1@cosmosbay.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Acked-by:

"David S. Miller" <davem@davemloft.net> Signed-off-by:

Andrew Morton <akpm@osdl.org> Signed-off-by:

Linus Torvalds <torvalds@osdl.org>

net/socket.c

+16 −3

Original line number	Diff line number	Diff line
		@@ -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;

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