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Date: Sun, 29 Jan 2012 17:49:38 +0200
From: Lucian Adrian Grijincu <lucian.grijincu@...il.com>
To: "Eric W. Biederman" <ebiederm@...ssion.com>
Cc: linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
netdev@...r.kernel.org,
Damien Millescamps <damien.millescamps@...nd.com>
Subject: Re: [PATCH 19/29] sysctl: Rewrite proc_sys_lookup introducing
find_entry and lookup_entry.
On Fri, Jan 27, 2012 at 6:51 AM, Eric W. Biederman
<ebiederm@...ssion.com> wrote:
> Replace the helpers that proc_sys_lookup uses with helpers that work
> in terms of an entire sysctl directory. This is worse for sysctl_lock
> hold times but it is much better for code clarity and the code cleanups
> to come.
>
> find_in_table is no longer needed so it is removed.
>
> find_entry a general helper to find entries in a directory is added.
>
> lookup_entry is a simple wrapper around find_entry that takes the
> sysctl_lock increases the use count if an entry is found and drops
> the sysctl_lock.
>
> Signed-off-by: Eric W. Biederman <ebiederm@...ssion.com>
> ---
> fs/proc/proc_sysctl.c | 102 ++++++++++++++++++++++++++++++++++++------------
> 1 files changed, 76 insertions(+), 26 deletions(-)
>
> diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
> index 88d1b06..3b63f29 100644
> --- a/fs/proc/proc_sysctl.c
> +++ b/fs/proc/proc_sysctl.c
> @@ -49,6 +49,55 @@ static struct ctl_table_root sysctl_table_root = {
>
> static DEFINE_SPINLOCK(sysctl_lock);
>
> +static int namecmp(const char *name1, int len1, const char *name2, int len2)
> +{
> + int minlen;
> + int cmp;
> +
> + minlen = len1;
> + if (minlen > len2)
> + minlen = len2;
> +
> + cmp = memcmp(name1, name2, minlen);
> + if (cmp == 0)
> + cmp = len1 - len2;
> + return cmp;
> +}
> +
I would add a note that this needs sysctl_lock as this requirement
remains valid in the final version of the code too:
/* called under sysctl_lock */
> +static struct ctl_table *find_entry(struct ctl_table_header **phead,
> + struct ctl_table_set *set,
> + struct ctl_table_header *dir_head, struct ctl_table *dir,
> + const char *name, int namelen)
> +{
> + struct ctl_table_header *head;
> + struct ctl_table *entry;
> +
> + if (dir_head->set == set) {
> + for (entry = dir; entry->procname; entry++) {
> + const char *procname = entry->procname;
> + if (namecmp(procname, strlen(procname), name, namelen) == 0) {
> + *phead = dir_head;
> + return entry;
> + }
> + }
> + }
> +
> + list_for_each_entry(head, &set->list, ctl_entry) {
> + if (head->unregistering)
> + continue;
> + if (head->attached_to != dir)
> + continue;
> + for (entry = head->attached_by; entry->procname; entry++) {
> + const char *procname = entry->procname;
> + if (namecmp(procname, strlen(procname), name, namelen) == 0) {
> + *phead = head;
> + return entry;
> + }
> + }
> + }
> + return NULL;
> +}
> +
> static void init_header(struct ctl_table_header *head,
> struct ctl_table_root *root, struct ctl_table_set *set,
> struct ctl_table *table)
> @@ -168,6 +217,32 @@ lookup_header_list(struct ctl_table_root *root, struct nsproxy *namespaces)
> return &set->list;
> }
>
> +static struct ctl_table *lookup_entry(struct ctl_table_header **phead,
> + struct ctl_table_header *dir_head,
> + struct ctl_table *dir,
> + const char *name, int namelen)
> +{
> + struct ctl_table_header *head;
> + struct ctl_table *entry;
> + struct ctl_table_root *root;
> + struct ctl_table_set *set;
> +
> + spin_lock(&sysctl_lock);
> + root = &sysctl_table_root;
> + do {
> + set = lookup_header_set(root, current->nsproxy);
> + entry = find_entry(&head, set, dir_head, dir, name, namelen);
> + if (entry && use_table(head))
> + *phead = head;
> + else
> + entry = NULL;
> + root = list_entry(root->root_list.next,
> + struct ctl_table_root, root_list);
> + } while (!entry && root != &sysctl_table_root);
> + spin_unlock(&sysctl_lock);
> + return entry;
> +}
> +
> static struct ctl_table_header *__sysctl_head_next(struct nsproxy *namespaces,
> struct ctl_table_header *prev)
> {
> @@ -284,21 +359,6 @@ out:
> return inode;
> }
>
> -static struct ctl_table *find_in_table(struct ctl_table *p, struct qstr *name)
> -{
> - for ( ; p->procname; p++) {
> - if (strlen(p->procname) != name->len)
> - continue;
> -
> - if (memcmp(p->procname, name->name, name->len) != 0)
> - continue;
> -
> - /* I have a match */
> - return p;
> - }
> - return NULL;
> -}
> -
> static struct ctl_table_header *grab_header(struct inode *inode)
> {
> struct ctl_table_header *head = PROC_I(inode)->sysctl;
> @@ -328,17 +388,7 @@ static struct dentry *proc_sys_lookup(struct inode *dir, struct dentry *dentry,
>
> table = table ? table->child : &head->ctl_table[1];
>
> - p = find_in_table(table, name);
> - if (!p) {
> - for (h = sysctl_head_next(NULL); h; h = sysctl_head_next(h)) {
> - if (h->attached_to != table)
> - continue;
> - p = find_in_table(h->attached_by, name);
> - if (p)
> - break;
> - }
> - }
> -
> + p = lookup_entry(&h, head, table, name->name, name->len);
> if (!p)
> goto out;
>
> --
> 1.7.2.5
>
--
.
..: Lucian
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