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Subject[PATCH v3 074/110] VFS: replace {, total_}link_count in task_struct with pointer to nameidata
Date
From: NeilBrown <neilb@suse.de>

task_struct currently contains two ad-hoc members for use by the VFS:
link_count and total_link_count. These are only interesting to fs/namei.c,
so exposing them explicitly is poor layering. Incidentally, link_count
isn't used anymore, so it can just die.

This patches replaces those with a single pointer to 'struct nameidata'.
This structure represents the current filename lookup of which
there can only be one per process, and is a natural place to
store total_link_count.

This will allow the current "nameidata" argument to all
follow_link operations to be removed as current->nameidata
can be used instead in the _very_ few instances that care about
it at all.

As there are occasional circumstances where pathname lookup can
recurse, such as through kern_path_locked, we always save and old
current->nameidata (if there is one) when setting a new value, and
make sure any active link_counts are preserved.

follow_mount and follow_automount now get a 'struct nameidata *'
rather than 'int flags' so that they can directly access
total_link_count, rather than going through 'current'.

Suggested-by: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
fs/namei.c | 70 ++++++++++++++++++++++++++++-----------------------
include/linux/sched.h | 2 +-
2 files changed, 40 insertions(+), 32 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index 046a703..699e093 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -505,6 +505,7 @@ struct nameidata {
unsigned seq, m_seq;
int last_type;
unsigned depth;
+ int total_link_count;
struct file *base;
struct saved {
struct path link;
@@ -513,16 +514,25 @@ struct nameidata {
} *stack, internal[EMBEDDED_LEVELS];
};

-static void set_nameidata(struct nameidata *nd)
+static struct nameidata *set_nameidata(struct nameidata *p)
{
- nd->stack = nd->internal;
+ struct nameidata *old = current->nameidata;
+ p->stack = p->internal;
+ p->total_link_count = old ? old->total_link_count : 0;
+ current->nameidata = p;
+ return old;
}

-static void restore_nameidata(struct nameidata *nd)
+static void restore_nameidata(struct nameidata *old)
{
- if (nd->stack != nd->internal) {
- kfree(nd->stack);
- nd->stack = nd->internal;
+ struct nameidata *now = current->nameidata;
+
+ current->nameidata = old;
+ if (old)
+ old->total_link_count = now->total_link_count;
+ if (now->stack != now->internal) {
+ kfree(now->stack);
+ now->stack = now->internal;
}
}

@@ -970,7 +980,7 @@ EXPORT_SYMBOL(follow_up);
* - return -EISDIR to tell follow_managed() to stop and return the path we
* were called with.
*/
-static int follow_automount(struct path *path, unsigned flags,
+static int follow_automount(struct path *path, struct nameidata *nd,
bool *need_mntput)
{
struct vfsmount *mnt;
@@ -990,13 +1000,13 @@ static int follow_automount(struct path *path, unsigned flags,
* as being automount points. These will need the attentions
* of the daemon to instantiate them before they can be used.
*/
- if (!(flags & (LOOKUP_PARENT | LOOKUP_DIRECTORY |
- LOOKUP_OPEN | LOOKUP_CREATE | LOOKUP_AUTOMOUNT)) &&
+ if (!(nd->flags & (LOOKUP_PARENT | LOOKUP_DIRECTORY |
+ LOOKUP_OPEN | LOOKUP_CREATE | LOOKUP_AUTOMOUNT)) &&
path->dentry->d_inode)
return -EISDIR;

- current->total_link_count++;
- if (current->total_link_count >= 40)
+ nd->total_link_count++;
+ if (nd->total_link_count >= 40)
return -ELOOP;

mnt = path->dentry->d_op->d_automount(path);
@@ -1010,7 +1020,7 @@ static int follow_automount(struct path *path, unsigned flags,
* the path being looked up; if it wasn't then the remainder of
* the path is inaccessible and we should say so.
*/
- if (PTR_ERR(mnt) == -EISDIR && (flags & LOOKUP_PARENT))
+ if (PTR_ERR(mnt) == -EISDIR && (nd->flags & LOOKUP_PARENT))
return -EREMOTE;
return PTR_ERR(mnt);
}
@@ -1050,7 +1060,7 @@ static int follow_automount(struct path *path, unsigned flags,
*
* Serialization is taken care of in namespace.c
*/
-static int follow_managed(struct path *path, unsigned flags)
+static int follow_managed(struct path *path, struct nameidata *nd)
{
struct vfsmount *mnt = path->mnt; /* held by caller, must be left alone */
unsigned managed;
@@ -1094,7 +1104,7 @@ static int follow_managed(struct path *path, unsigned flags)

/* Handle an automount point */
if (managed & DCACHE_NEED_AUTOMOUNT) {
- ret = follow_automount(path, flags, &need_mntput);
+ ret = follow_automount(path, nd, &need_mntput);
if (ret < 0)
break;
continue;
@@ -1483,7 +1493,7 @@ unlazy:
}
path->mnt = mnt;
path->dentry = dentry;
- err = follow_managed(path, nd->flags);
+ err = follow_managed(path, nd);
if (unlikely(err < 0)) {
path_put_conditional(path, nd);
return err;
@@ -1513,7 +1523,7 @@ static int lookup_slow(struct nameidata *nd, struct path *path)
return PTR_ERR(dentry);
path->mnt = nd->path.mnt;
path->dentry = dentry;
- err = follow_managed(path, nd->flags);
+ err = follow_managed(path, nd);
if (unlikely(err < 0)) {
path_put_conditional(path, nd);
return err;
@@ -1563,7 +1573,7 @@ static void terminate_walk(struct nameidata *nd)
static int pick_link(struct nameidata *nd, struct path *link)
{
int error;
- if (unlikely(current->total_link_count++ >= MAXSYMLINKS)) {
+ if (unlikely(nd->total_link_count++ >= MAXSYMLINKS)) {
path_to_nameidata(link, nd);
return -ELOOP;
}
@@ -1981,7 +1991,7 @@ static int path_init(int dfd, const struct filename *name, unsigned int flags,
rcu_read_unlock();
return -ECHILD;
done:
- current->total_link_count = 0;
+ nd->total_link_count = 0;
return link_path_walk(s, nd);
}

@@ -2087,10 +2097,9 @@ static int filename_lookup(int dfd, struct filename *name,
unsigned int flags, struct nameidata *nd)
{
int retval;
+ struct nameidata *saved_nd = set_nameidata(nd);

- set_nameidata(nd);
retval = path_lookupat(dfd, name, flags | LOOKUP_RCU, nd);
-
if (unlikely(retval == -ECHILD))
retval = path_lookupat(dfd, name, flags, nd);
if (unlikely(retval == -ESTALE))
@@ -2098,7 +2107,7 @@ static int filename_lookup(int dfd, struct filename *name,

if (likely(!retval))
audit_inode(name, nd->path.dentry, flags & LOOKUP_PARENT);
- restore_nameidata(nd);
+ restore_nameidata(saved_nd);
return retval;
}

@@ -2426,11 +2435,11 @@ static int
filename_mountpoint(int dfd, struct filename *name, struct path *path,
unsigned int flags)
{
- struct nameidata nd;
+ struct nameidata nd, *saved;
int error;
if (IS_ERR(name))
return PTR_ERR(name);
- set_nameidata(&nd);
+ saved = set_nameidata(&nd);
error = path_mountpoint(dfd, name, path, &nd, flags | LOOKUP_RCU);
if (unlikely(error == -ECHILD))
error = path_mountpoint(dfd, name, path, &nd, flags);
@@ -2438,7 +2447,7 @@ filename_mountpoint(int dfd, struct filename *name, struct path *path,
error = path_mountpoint(dfd, name, path, &nd, flags | LOOKUP_REVAL);
if (likely(!error))
audit_inode(name, path->dentry, 0);
- restore_nameidata(&nd);
+ restore_nameidata(saved);
putname(name);
return error;
}
@@ -3087,7 +3096,7 @@ retry_lookup:
if ((open_flag & (O_EXCL | O_CREAT)) == (O_EXCL | O_CREAT))
goto exit_dput;

- error = follow_managed(&path, nd->flags);
+ error = follow_managed(&path, nd);
if (error < 0)
goto exit_dput;

@@ -3323,31 +3332,29 @@ out2:
struct file *do_filp_open(int dfd, struct filename *pathname,
const struct open_flags *op)
{
- struct nameidata nd;
+ struct nameidata nd, *saved_nd = set_nameidata(&nd);
int flags = op->lookup_flags;
struct file *filp;

- set_nameidata(&nd);
filp = path_openat(dfd, pathname, &nd, op, flags | LOOKUP_RCU);
if (unlikely(filp == ERR_PTR(-ECHILD)))
filp = path_openat(dfd, pathname, &nd, op, flags);
if (unlikely(filp == ERR_PTR(-ESTALE)))
filp = path_openat(dfd, pathname, &nd, op, flags | LOOKUP_REVAL);
- restore_nameidata(&nd);
+ restore_nameidata(saved_nd);
return filp;
}

struct file *do_file_open_root(struct dentry *dentry, struct vfsmount *mnt,
const char *name, const struct open_flags *op)
{
- struct nameidata nd;
+ struct nameidata nd, *saved_nd;
struct file *file;
struct filename *filename;
int flags = op->lookup_flags | LOOKUP_ROOT;

nd.root.mnt = mnt;
nd.root.dentry = dentry;
- set_nameidata(&nd);

if (d_is_symlink(dentry) && op->intent & LOOKUP_OPEN)
return ERR_PTR(-ELOOP);
@@ -3356,12 +3363,13 @@ struct file *do_file_open_root(struct dentry *dentry, struct vfsmount *mnt,
if (unlikely(IS_ERR(filename)))
return ERR_CAST(filename);

+ saved_nd = set_nameidata(&nd);
file = path_openat(-1, filename, &nd, op, flags | LOOKUP_RCU);
if (unlikely(file == ERR_PTR(-ECHILD)))
file = path_openat(-1, filename, &nd, op, flags);
if (unlikely(file == ERR_PTR(-ESTALE)))
file = path_openat(-1, filename, &nd, op, flags | LOOKUP_REVAL);
- restore_nameidata(&nd);
+ restore_nameidata(saved_nd);
putname(filename);
return file;
}
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 26a2e61..f6c9b69 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1461,7 +1461,7 @@ struct task_struct {
it with task_lock())
- initialized normally by setup_new_exec */
/* file system info */
- int link_count, total_link_count;
+ struct nameidata *nameidata;
#ifdef CONFIG_SYSVIPC
/* ipc stuff */
struct sysv_sem sysvsem;
--
2.1.4


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