Sometimes it might be desirable to prohibit removing a symbolic link
in configfs. One example is USB gadget: when a gadget is already bound,
if USB function symlink (used to associate USB functions with USB
configurations) is removed, the gadget must be thrown away, too.
A better solution would be to fail with e.g. -EBUSY.
Why add a new method? Even though (*drop_link)() does have a return value,
it is ignored in fs/configfs/symlink.c:configfs_unlink(). It could be
tempting to just check the return value, but some users of configfs might
already depend on the fact that (*drop_link)() is called _after_
corresponding filesystem entities are torn down. In other words, the
semantics of (*drop_link)() is "the final, unconditional cleanup". In order
not to break this semantics, a new method is added and its value is checked
in fs/configfs/symlink.c:configfs_unlink().
Signed-off-by: Andrzej Pietrasiewicz <andrzej.p@xxxxxxxxxxx>
---
fs/configfs/symlink.c | 11 +++++++++--
include/linux/configfs.h | 1 +
2 files changed, 10 insertions(+), 2 deletions(-)
diff --git a/fs/configfs/symlink.c b/fs/configfs/symlink.c
index cc9f254..52851dc 100644
--- a/fs/configfs/symlink.c
+++ b/fs/configfs/symlink.c
@@ -198,6 +198,13 @@ int configfs_unlink(struct inode *dir, struct dentry *dentry)
parent_item = configfs_get_config_item(dentry->d_parent);
type = parent_item->ci_type;
+ if (type && type->ct_item_ops &&
+ type->ct_item_ops->allow_drop) {
+ ret = type->ct_item_ops->allow_drop(parent_item,
+ sl->sl_target);
+ if (ret)
+ goto out_put;
+ }
spin_lock(&configfs_dirent_lock);
list_del_init(&sd->s_sibling);
@@ -224,10 +231,10 @@ int configfs_unlink(struct inode *dir, struct dentry *dentry)
config_item_put(sl->sl_target);
kfree(sl);
- config_item_put(parent_item);
-
ret = 0;
+out_put:
+ config_item_put(parent_item);
out:
return ret;
}
diff --git a/include/linux/configfs.h b/include/linux/configfs.h
index 34025df..29df5e1 100644
--- a/include/linux/configfs.h
+++ b/include/linux/configfs.h
@@ -226,6 +226,7 @@ struct configfs_item_operations {
ssize_t (*show_attribute)(struct config_item *, struct configfs_attribute *,char *);
ssize_t (*store_attribute)(struct config_item *,struct configfs_attribute *,const char *, size_t);
int (*allow_link)(struct config_item *src, struct config_item *target);
+ int (*allow_drop)(struct config_item *src, struct config_item *target);
int (*drop_link)(struct config_item *src, struct config_item *target);
};
--
1.9.1
--
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