Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932362Ab0FYTHF (ORCPT ); Fri, 25 Jun 2010 15:07:05 -0400 Received: from mx1.redhat.com ([209.132.183.28]:46655 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932423Ab0FYTGx (ORCPT ); Fri, 25 Jun 2010 15:06:53 -0400 From: Valerie Aurora To: Alexander Viro Cc: Miklos Szeredi , Jan Blunck , Christoph Hellwig , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Valerie Aurora Subject: [PATCH 22/38] union-mount: Implement union lookup Date: Fri, 25 Jun 2010 12:05:12 -0700 Message-Id: <1277492728-11446-23-git-send-email-vaurora@redhat.com> In-Reply-To: <1277492728-11446-1-git-send-email-vaurora@redhat.com> References: <1277492728-11446-1-git-send-email-vaurora@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 10963 Lines: 376 Implement unioned directories, whiteouts, and fallthrus in pathname lookup routines. do_lookup() and lookup_hash() call lookup_union() after looking up the dentry from the top-level file system. lookup_union() is centered around __lookup_hash(), which does cached and/or real lookups and revalidates each dentry in the union stack. XXX - implement negative union cache entries XXX - What about different permissions on different layers on the same directory name? Should complain, fail, test permissions on all layers, what? --- fs/namei.c | 174 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++- fs/union.c | 94 ++++++++++++++++++++++++++++++++ fs/union.h | 7 +++ 3 files changed, 274 insertions(+), 1 deletions(-) diff --git a/fs/namei.c b/fs/namei.c index 06aad7e..3f969af 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -35,6 +35,7 @@ #include #include "internal.h" +#include "union.h" /* [Feb-1997 T. Schoebel-Theuer] * Fundamental changes in the pathname lookup mechanisms (namei) @@ -722,6 +723,163 @@ static __always_inline void follow_dotdot(struct nameidata *nd) follow_mount(&nd->path); } +static struct dentry *__lookup_hash(struct qstr *name, struct dentry *base, + struct nameidata *nd); + +/* + * __lookup_union - Given a path from the topmost layer, lookup and + * revalidate each dentry in its union stack, building it if necessary + * + * @nd - nameidata for the parent of @topmost + * @name - pathname from this element on + * @topmost - path of the topmost matching dentry + * + * Given the nameidata and the path of the topmost dentry for this + * pathname, lookup, revalidate, and build the associated union stack. + * @topmost must be either a negative dentry or a directory, and not a + * whiteout. + * + * This function may stomp nd->path with the path of the parent + * directory of lower layer, so the caller must save nd->path and + * restore it afterwards. You probably want to use lookup_union(), + * not __lookup_union(). + */ + +static int __lookup_union(struct nameidata *nd, struct qstr *name, + struct path *topmost) +{ + struct path parent = nd->path; + struct path lower, upper; + struct union_dir *ud; + /* new_ud is the tail of the list of union dirs for this dentry */ + struct union_dir **next_ud = &topmost->dentry->d_union_dir; + int err = 0; + + /* + * upper is either a negative dentry from the top layer, or it + * is the most recent positive dentry for a directory that + * we've seen. + */ + upper = *topmost; + + /* Go through each dir underlying the parent, looking for a match */ + for (ud = nd->path.dentry->d_union_dir; ud != NULL; ud = ud->u_lower) { + BUG_ON(ud->u_this.dentry->d_count.counter == 0); + /* Change the nameidata to point to this level's dir */ + nd->path = ud->u_this; + /* Lookup the child in this level */ + lower.mnt = mntget(nd->path.mnt); + mutex_lock(&nd->path.dentry->d_inode->i_mutex); + lower.dentry = __lookup_hash(name, nd->path.dentry, nd); + mutex_unlock(&nd->path.dentry->d_inode->i_mutex); + + if (IS_ERR(lower.dentry)) { + mntput(lower.mnt); + err = PTR_ERR(lower.dentry); + goto out; + } + + if (!lower.dentry->d_inode) { + if (d_is_whiteout(lower.dentry)) + break; + if (IS_OPAQUE(nd->path.dentry->d_inode) && + !d_is_fallthru(lower.dentry)) + break; + /* Plain old negative! Keep looking */ + path_put(&lower); + continue; + } + + /* Finding a non-dir ends the lookup, one way or another */ + if (!S_ISDIR(lower.dentry->d_inode->i_mode)) { + /* Ignore file below dir - invalid */ + if (upper.dentry->d_inode && + S_ISDIR(upper.dentry->d_inode->i_mode)) { + path_put(&lower); + break; + } + /* Bingo, found our target */ + dput(topmost->dentry); + /* mntput(topmost) done in link_path_walk() */ + *topmost = lower; + break; + } + + /* Allow read-only submounts on lower layers */ + follow_mount(&lower); + + /* Found a directory. Create the topmost version if it doesn't exist */ + if (!topmost->dentry->d_inode) { + err = union_create_topmost_dir(&parent, name, topmost, + &lower); + if (err) { + path_put(&lower); + return err; + } + } + + err = union_add_dir(&upper, &lower, next_ud); + if (err) + break; + + next_ud = &(*next_ud)->u_lower; + upper = lower; + } +out: + return 0; +} + +/* + * lookup_union - revalidate and build union stack for this path + * + * We borrow the nameidata struct from the topmost layer to do the + * revalidation on lower dentries, replacing the topmost parent + * directory's path with that of the matching parent dir in each lower + * layer. This wrapper for __lookup_union() saves the topmost layer's + * path and restores it when we are done. + */ +static int lookup_union(struct nameidata *nd, struct qstr *name, + struct path *topmost) +{ + struct path saved_path; + int err; + + BUG_ON(!IS_MNT_UNION(nd->path.mnt) && !IS_MNT_UNION(topmost->mnt)); + BUG_ON(!mutex_is_locked(&nd->path.dentry->d_inode->i_mutex)); + + saved_path = nd->path; + path_get(&saved_path); + + err = __lookup_union(nd, name, topmost); + + nd->path = saved_path; + path_put(&saved_path); + + return err; +} + +/* + * do_union_lookup - union mount-aware part of do_lookup + * + * do_lookup()-style wrapper for lookup_union(). Follows mounts. + */ + +static int do_lookup_union(struct nameidata *nd, struct qstr *name, + struct path *topmost) +{ + struct dentry *parent = nd->path.dentry; + struct inode *dir = parent->d_inode; + int err; + + mutex_lock(&dir->i_mutex); + err = lookup_union(nd, name, topmost); + mutex_unlock(&dir->i_mutex); + + __follow_mount(topmost); + + return err; +} + /* * It's more convoluted than I'd like it to be, but... it's still fairly * small and for now I'd prefer to have fast path as straight as possible. @@ -752,6 +910,11 @@ done: path->mnt = mnt; path->dentry = dentry; __follow_mount(path); + if (needs_lookup_union(&nd->path, path)) { + int err = do_lookup_union(nd, name, path); + if (err < 0) + return err; + } return 0; need_lookup: @@ -1223,8 +1386,13 @@ static int lookup_hash(struct nameidata *nd, struct qstr *name, err = PTR_ERR(path->dentry); path->dentry = NULL; path->mnt = NULL; + return err; } + + if (needs_lookup_union(&nd->path, path)) + err = lookup_union(nd, name, path); return err; + } static int __lookup_one_len(const char *name, struct qstr *this, @@ -2888,7 +3056,11 @@ SYSCALL_DEFINE4(renameat, int, olddfd, const char __user *, oldname, error = -EXDEV; if (oldnd.path.mnt != newnd.path.mnt) goto exit2; - + /* Rename on union mounts not implemented yet */ + /* XXX much harsher check than necessary - can do some renames */ + if (IS_DIR_UNIONED(oldnd.path.dentry) || + IS_DIR_UNIONED(newnd.path.dentry)) + goto exit2; old_dir = oldnd.path.dentry; error = -EBUSY; if (oldnd.last_type != LAST_NORM) diff --git a/fs/union.c b/fs/union.c index 02abb7c..c089c02 100644 --- a/fs/union.c +++ b/fs/union.c @@ -21,6 +21,7 @@ #include #include #include +#include #include "union.h" @@ -117,3 +118,96 @@ void d_free_unions(struct dentry *dentry) } dentry->d_union_dir = NULL; } + +/** + * needs_lookup_union - Avoid union lookup when not necessary + * + * @parent_path: path of the parent directory + * @path: path of the lookup target + * + * Check to see if the target needs union lookup. Two cases need + * union lookup: the target is a directory, and the target is a + * negative dentry. + * + * Returns 0 if this dentry is definitely not unioned. Returns 1 if + * it is possible this dentry is unioned. + */ + +int needs_lookup_union(struct path *parent_path, struct path *path) +{ + /* + * If the target is the root of the mount, then its union + * stack was already created at mount time (if this is a union + * mount). + */ + if (IS_ROOT(path->dentry)) + return 0; + + /* Only dentries in a unioned directory need a union lookup. */ + if (!IS_DIR_UNIONED(parent_path->dentry)) + return 0; + + /* Whiteouts cover up everything below */ + if (d_is_whiteout(path->dentry)) + return 0; + + /* Opaque dirs cover except if this is a fallthru */ + if (IS_OPAQUE(parent_path->dentry->d_inode) && + !d_is_fallthru(path->dentry)) + return 0; + + /* + * XXX Negative dentries in unioned directories must always go + * through a full union lookup because there might be a + * matching entry below it. To improve performance, we should + * mark negative dentries in some way to show they have + * already been looked up in the union and nothing was found. + * Maybe mark it opaque? + */ + if (!path->dentry->d_inode) + return 1; + + /* + * If it's not a directory and it's a positive dentry, then we + * already have the topmost dentry and we don't need to do any + * lookup in lower layers. + */ + + if (!S_ISDIR(path->dentry->d_inode->i_mode)) + return 0; + + /* Is the union stack already constructed? */ + if (IS_DIR_UNIONED(path->dentry)) + return 0; + + /* + * XXX This is like the negative dentry case. This directory + * may have no matching directories in the lower layers, or + * this may just be the first time we looked it up. We can't + * tell the difference. + */ + return 1; +} + +/* + * union_create_topmost_dir - Create a matching dir in the topmost file system + */ + +int union_create_topmost_dir(struct path *parent, struct qstr *name, + struct path *topmost, struct path *lower) +{ + int mode = lower->dentry->d_inode->i_mode; + int res; + + BUG_ON(topmost->dentry->d_inode); + + res = mnt_want_write(parent->mnt); + if (res) + return res; + + res = vfs_mkdir(parent->dentry->d_inode, topmost->dentry, mode); + + mnt_drop_write(parent->mnt); + + return res; +} diff --git a/fs/union.h b/fs/union.h index 04efc1f..505f132 100644 --- a/fs/union.h +++ b/fs/union.h @@ -51,15 +51,22 @@ struct union_dir { }; #define IS_MNT_UNION(mnt) ((mnt)->mnt_flags & MNT_UNION) +#define IS_DIR_UNIONED(dentry) ((dentry)->d_union_dir) extern int union_add_dir(struct path *, struct path *, struct union_dir **); extern void d_free_unions(struct dentry *); +int needs_lookup_union(struct path *, struct path *); +int union_create_topmost_dir(struct path *, struct qstr *, struct path *, + struct path *); #else /* CONFIG_UNION_MOUNT */ #define IS_MNT_UNION(x) (0) +#define IS_DIR_UNIONED(x) (0) #define union_add_dir(x, y, z) ({ BUG(); (NULL); }) #define d_free_unions(x) do { } while (0) +#define needs_lookup_union(x, y) ({ (0); }) +#define union_create_topmost_dir(w, x, y, z) ({ BUG(); (NULL); }) #endif /* CONFIG_UNION_MOUNT */ #endif /* __KERNEL__ */ -- 1.6.3.3 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/