Messages in this thread Patch in this message | | | Date | Wed, 21 Apr 2004 15:41:04 +0530 | From | Maneesh Soni <> | Subject | Re: [RFC] fix sysfs symlinks |
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On Tue, Apr 20, 2004 at 09:16:02AM -0700, Greg KH wrote: > On Sat, Apr 17, 2004 at 09:22:06AM +0100, viro@parcelfarce.linux.theplanet.co.uk wrote: > > On Sat, Apr 17, 2004 at 09:07:12AM +0100, Russell King wrote: > > > What about other bus types? Do I really need to teach userspace about > > > the relationships between all the various bus types we have on ARM and > > > how to work out what these relationships are by guessing? > > > > > > Please. The symlinks are necessary and they are the sole source of > > > the relationship information. > > > > In which case you want them to be associated with target, not the current > > pathname of target. And no, I don't buy the "so far all renames happen *here* > > and all symlinks are pointing *there*, so we don't care" - that won't last. > > > > When do we have a legitimate reason for dangling symlinks in sysfs, anyway? > > Ok, in thinking about it some more, we don't. And I don't have a > problem with grabbing the reference to the target anymore either (after > looking over the code). So no more objections from me about this :) >
Please see the patch below against 2.6.6-rc2-mm1. In the last version I missed releasing the target kobject whenever link is deleted. I have corrected this now. Sorry for the missing code and please review again.
Regards Maneesh
o The symlinks code in sysfs doesnot point to the correct target kobject whenever target kobject is renamed and suffers from dangling symlinks if target kobject is removed.
o The following patch implements ->readlink and ->follow_link operations for sysfs instead of using the page_symlink_inode_operations. The pointer to target kobject is saved in the link dentry's d_fsdata field. The target path is generated everytime we do ->readlink and ->follow_link. This results in generating the correct target path during readlink and follow_link operations inspite of renamed target kobject.
o This also pins the target kobject during link creation and the ref. is released when the link is removed.
o Apart from being correct this patch also saves some memory by not pinning a whole page for saving the target information.
fs/sysfs/dir.c | 6 ++ fs/sysfs/inode.c | 5 + fs/sysfs/symlink.c | 135 +++++++++++++++++++++++++++++++++++++---------------- fs/sysfs/sysfs.h | 2 4 files changed, 108 insertions(+), 40 deletions(-)
diff -puN fs/sysfs/sysfs.h~sysfs-symlinks-fix fs/sysfs/sysfs.h --- linux-2.6.6-rc2-mm1/fs/sysfs/sysfs.h~sysfs-symlinks-fix 2004-04-21 14:59:13.000000000 +0530 +++ linux-2.6.6-rc2-mm1-maneesh/fs/sysfs/sysfs.h 2004-04-21 15:00:08.000000000 +0530 @@ -12,6 +12,8 @@ extern void sysfs_hash_and_remove(struct extern int sysfs_create_subdir(struct kobject *, const char *, struct dentry **); extern void sysfs_remove_subdir(struct dentry *); +extern int sysfs_readlink(struct dentry *, char __user *, int ); +extern int sysfs_follow_link(struct dentry *, struct nameidata *); static inline struct kobject *sysfs_get_kobject(struct dentry *dentry) { diff -puN fs/sysfs/dir.c~sysfs-symlinks-fix fs/sysfs/dir.c --- linux-2.6.6-rc2-mm1/fs/sysfs/dir.c~sysfs-symlinks-fix 2004-04-21 14:59:22.000000000 +0530 +++ linux-2.6.6-rc2-mm1-maneesh/fs/sysfs/dir.c 2004-04-21 15:39:30.000000000 +0530 @@ -135,6 +135,12 @@ restart: * Unlink and unhash. */ spin_unlock(&dcache_lock); + /* release the target kobject in case of + * a symlink + */ + if (S_ISLNK(d->d_inode->i_mode)) + kobject_put(d->d_fsdata); + d_delete(d); simple_unlink(dentry->d_inode,d); dput(d); diff -puN fs/sysfs/inode.c~sysfs-symlinks-fix fs/sysfs/inode.c --- linux-2.6.6-rc2-mm1/fs/sysfs/inode.c~sysfs-symlinks-fix 2004-04-21 14:59:25.000000000 +0530 +++ linux-2.6.6-rc2-mm1-maneesh/fs/sysfs/inode.c 2004-04-21 15:39:20.000000000 +0530 @@ -96,6 +96,11 @@ void sysfs_hash_and_remove(struct dentry pr_debug("sysfs: Removing %s (%d)\n", victim->d_name.name, atomic_read(&victim->d_count)); + /* release the target kobject in case of + * a symlink + */ + if (S_ISLNK(victim->d_inode->i_mode)) + kobject_put(victim->d_fsdata); d_delete(victim); simple_unlink(dir->d_inode,victim); } diff -puN fs/sysfs/symlink.c~sysfs-symlinks-fix fs/sysfs/symlink.c --- linux-2.6.6-rc2-mm1/fs/sysfs/symlink.c~sysfs-symlinks-fix 2004-04-21 14:59:28.000000000 +0530 +++ linux-2.6.6-rc2-mm1-maneesh/fs/sysfs/symlink.c 2004-04-21 15:39:51.000000000 +0530 @@ -8,27 +8,17 @@ #include "sysfs.h" +static struct inode_operations sysfs_symlink_inode_operations = { + .readlink = sysfs_readlink, + .follow_link = sysfs_follow_link, +}; static int init_symlink(struct inode * inode) { - inode->i_op = &page_symlink_inode_operations; + inode->i_op = &sysfs_symlink_inode_operations; return 0; } -static int sysfs_symlink(struct inode * dir, struct dentry *dentry, const char * symname) -{ - int error; - - error = sysfs_create(dentry, S_IFLNK|S_IRWXUGO, init_symlink); - if (!error) { - int l = strlen(symname)+1; - error = page_symlink(dentry->d_inode, symname, l); - if (error) - iput(dentry->d_inode); - } - return error; -} - static int object_depth(struct kobject * kobj) { struct kobject * p = kobj; @@ -74,37 +64,20 @@ int sysfs_create_link(struct kobject * k struct dentry * dentry = kobj->dentry; struct dentry * d; int error = 0; - int size; - int depth; - char * path; - char * s; - - depth = object_depth(kobj); - size = object_path_length(target) + depth * 3 - 1; - if (size > PATH_MAX) - return -ENAMETOOLONG; - pr_debug("%s: depth = %d, size = %d\n",__FUNCTION__,depth,size); - - path = kmalloc(size,GFP_KERNEL); - if (!path) - return -ENOMEM; - memset(path,0,size); - - for (s = path; depth--; s += 3) - strcpy(s,"../"); - - fill_object_path(target,path,size); - pr_debug("%s: path = '%s'\n",__FUNCTION__,path); down(&dentry->d_inode->i_sem); d = sysfs_get_dentry(dentry,name); - if (!IS_ERR(d)) - error = sysfs_symlink(dentry->d_inode,d,path); - else + if (!IS_ERR(d)) { + error = sysfs_create(d, S_IFLNK|S_IRWXUGO, init_symlink); + if (!error) + /* + * associate the link dentry with the target kobject + */ + d->d_fsdata = kobject_get(target); + } else error = PTR_ERR(d); dput(d); up(&dentry->d_inode->i_sem); - kfree(path); return error; } @@ -120,6 +93,88 @@ void sysfs_remove_link(struct kobject * sysfs_hash_and_remove(kobj->dentry,name); } +static int sysfs_get_target_path(struct kobject * kobj, struct kobject * target, + char *path) +{ + char * s; + int depth, size; + + depth = object_depth(kobj); + size = object_path_length(target) + depth * 3 - 1; + if (size > PATH_MAX) + return -ENAMETOOLONG; + + pr_debug("%s: depth = %d, size = %d\n", __FUNCTION__, depth, size); + + for (s = path; depth--; s += 3) + strcpy(s,"../"); + + fill_object_path(target, path, size); + pr_debug("%s: path = '%s'\n", __FUNCTION__, path); + + return 0; +} + +static int sysfs_getlink(struct dentry *dentry, char * path) +{ + struct kobject *kobj, *target_kobj; + struct dentry * target_parent; + int error = 0; + + kobj = sysfs_get_kobject(dentry->d_parent); + if (!kobj) + return -EINVAL; + + target_kobj = sysfs_get_kobject(dentry); + if (!target_kobj) { + kobject_put(kobj); + return -EINVAL; + } + target_parent = target_kobj->dentry->d_parent; + + down(&target_parent->d_inode->i_sem); + error = sysfs_get_target_path(kobj, target_kobj, path); + up(&target_parent->d_inode->i_sem); + + kobject_put(kobj); + kobject_put(target_kobj); + return error; + +} + +int sysfs_readlink(struct dentry *dentry, char __user *buffer, int buflen) +{ + int error = 0; + unsigned long page = get_zeroed_page(GFP_KERNEL); + + if (!page) + return -ENOMEM; + + error = sysfs_getlink(dentry, (char *) page); + if (!error) + error = vfs_readlink(dentry, buffer, buflen, (char *) page); + + free_page(page); + + return error; +} + +int sysfs_follow_link(struct dentry *dentry, struct nameidata *nd) +{ + int error = 0; + unsigned long page = get_zeroed_page(GFP_KERNEL); + + if (!page) + return -ENOMEM; + + error = sysfs_getlink(dentry, (char *) page); + if (!error) + error = vfs_follow_link(nd, (char *) page); + + free_page(page); + + return error; +} EXPORT_SYMBOL(sysfs_create_link); EXPORT_SYMBOL(sysfs_remove_link); _ -- Maneesh Soni Linux Technology Center, IBM Software Lab, Bangalore, India email: maneesh@in.ibm.com Phone: 91-80-25044999 Fax: 91-80-25268553 T/L : 9243696 - 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/
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