add two inotify_add_watch flags
PATCH 1/1 add two inotify_add_watch flags
Yo,
The below patch lets user space have more control over the inodes that inotify will watch. It introduces two new flags.
IN_ONLYDIR -- only watch the inode if it is a directory This is needed to avoid the race that can occur when we want to be sure
that we are watching a directory.
IN_DONT_FOLLOW -- don't follow a symlink. In combination withIN_ONLYDIR we can make sure that we don't watch the target of symlinks.
The issues the flags fix came up when writing the gnome-vfs inotify backend. Default behaviour is unchanged.
fs/inotify.c +10 -3
@@ -363,11 +363,18 @@/* * find_inode - resolve a user-given path to a specific inode and return a nd */ -static int find_inode (const char __user *dirname,struct nameidata *nd) +static int find_inode (const char __user *dirname,struct nameidata *nd, +int only_dir,int dont_follow_symlink) {int error; +unsigned flags =0 ; - error =__user_walk (dirname,LOOKUP_FOLLOW , nd); +if (!dont_follow_symlink) + flags |=LOOKUP_FOLLOW ; +if (only_dir) + flags |=LOOKUP_DIRECTORY ; + + error =__user_walk (dirname, flags, nd);if (error)return error;/* you can only watch an inode if you have read permissions on it */
@@ -943,7 +950,7 @@ goto fput_and_out; } - ret =find_inode (path, &nd); + ret =find_inode (path, &nd, mask &IN_ONLYDIR , mask &IN_DONT_FOLLOW );if (unlikely (ret)) goto fput_and_out;
include/linux/inotify.h +2 -0
@@ -47,6 +47,8 @@#define IN_MOVE (IN_MOVED_FROM | IN_MOVED_TO)/* moves */ /* special flags */ +#define IN_ONLYDIR 0x01000000/* only watch the path if it is a directory */ +#define IN_DONT_FOLLOW 0x02000000/* don't follow a sym link */ #define IN_MASK_ADD 0x20000000/* add to the mask of an already existing watch */ #define IN_ISDIR 0x40000000/* event occurred against dir */ #define IN_ONESHOT 0x80000000/* only send event once */
Quoted 7 lines · John McCutchan
The below patch lets user space have more control over the inodes that inotify will watch. It introduces two new flags.
IN_ONLYDIR-- only watch the inode if it is a directory This is needed to avoid the race that can occur when we want to be sure
that we are watching a directory.
Quoted 5 lines
IN_DONT_FOLLOW-- don't follow a symlink. In combination withIN_ONLYDIRwe can make sure that we don't watch the target of symlinks.The issues the flags fix came up when writing the gnome-vfs inotify backend. Default behaviour is unchanged.
Looks good to me, and I confirm we hit these issues in real-life with gnome-vfs.
Robert Love
Quoted 19 lines · John McCutchan
fs/inotify.c +9
-2-static int find_inode (const char __user *dirname,struct nameidata *nd) +static int find_inode (const char __user *dirname,struct nameidata *nd, +int only_dir,int dont_follow_symlink) {int error; +unsigned flags =0 ; - error =__user_walk (dirname,LOOKUP_FOLLOW , nd); +if (!dont_follow_symlink) + flags |=LOOKUP_FOLLOW ; +if (only_dir) + flags |=LOOKUP_DIRECTORY ; + + error =__user_walk (dirname, flags, nd);if (error)return error;/* you can only watch an inode if you have read permissions on it */
fs/inotify.c line 955
Quoted 7 lines
fs/inotify.c +1
-1@@ -943,7 +950,7 @@ goto fput_and_out; } - ret =find_inode (path, &nd); + ret =find_inode (path, &nd, mask &IN_ONLYDIR , mask &IN_DONT_FOLLOW );if (unlikely (ret)) goto fput_and_out;
I'd have thought that it'd be more general to pass the __user_walk flags into find_inode(), rather than calculating them in the callee. Slightly more efficient too.
Quoted 23 lines · Andrew Morton
Quoted 22 lines · John McCutchan
(quoted diff) +9
-2-static int find_inode(const char __user *dirname, struct nameidata *nd) +static int find_inode(const char __user *dirname, struct nameidata *nd, + int only_dir, int dont_follow_symlink) { int error; + unsigned flags = 0; - error = __user_walk(dirname, LOOKUP_FOLLOW, nd); + if (!dont_follow_symlink) + flags |= LOOKUP_FOLLOW; + if (only_dir) + flags |= LOOKUP_DIRECTORY; + + error = __user_walk(dirname, flags, nd); if (error) return error; /* you can only watch an inode if you have read permissions on it */@@ -943,7 +950,7 @@ goto fput_and_out; }
Quoted 8 lines
Review line 955
Quoted 4 lines
(quoted diff) +1
-1- ret = find_inode(path, &nd); + ret = find_inode(path, &nd, mask & IN_ONLYDIR, mask & IN_DONT_FOLLOW); if (unlikely(ret)) goto fput_and_out;I'd have thought that it'd be more general to pass the
__user_walkflags intofind_inode(), rather than calculating them in the callee. Slightly more efficient too.
Makes sense.
fs/inotify.c +10 -3
@@ -363,11 +363,12 @@/* * find_inode - resolve a user-given path to a specific inode and return a nd */ -static int find_inode (const char __user *dirname,struct nameidata *nd) +static int find_inode (const char __user *dirname,struct nameidata *nd, +unsigned flags) {int error; - error =__user_walk (dirname,LOOKUP_FOLLOW , nd); + error =__user_walk (dirname, flags, nd);if (error)return error;/* you can only watch an inode if you have read permissions on it */
@@ -932,6 +933,7 @@struct file *filp;int ret, fput_needed;int mask_add =0 ; +unsigned flags =0 ; filp =fget_light (fd, &fput_needed);if (unlikely (!filp))
@@ -943,7 +945,12 @@ goto fput_and_out; } - ret =find_inode (path, &nd); +if (!(mask &IN_DONT_FOLLOW )) + flags |=LOOKUP_FOLLOW ; +if (mask &IN_ONLYDIR ) + flags |=LOOKUP_DIRECTORY ; + + ret =find_inode (path, &nd, flags);if (unlikely (ret)) goto fput_and_out;
include/linux/inotify.h +2 -0
@@ -47,6 +47,8 @@#define IN_MOVE (IN_MOVED_FROM | IN_MOVED_TO)/* moves */ /* special flags */ +#define IN_ONLYDIR 0x01000000/* only watch the path if it is a directory */ +#define IN_DONT_FOLLOW 0x02000000/* don't follow a sym link */ #define IN_MASK_ADD 0x20000000/* add to the mask of an already existing watch */ #define IN_ISDIR 0x40000000/* event occurred against dir */ #define IN_ONESHOT 0x80000000/* only send event once */