From 756daf263ea53a8bfc89db26cb92e963953253a1 Mon Sep 17 00:00:00 2001 From: NeilBrown Date: Mon, 23 Mar 2015 13:37:38 +1100 Subject: [PATCH] VFS: replace {, total_}link_count in task_struct with pointer to nameidata 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 Signed-off-by: NeilBrown Signed-off-by: Al Viro --- 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 046a703c081d..699e093f52b5 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 26a2e6122734..f6c9b69d66f2 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; -- 2.30.2