replace ->follow_link() with new method that could stay in RCU mode

new method: ->get_link(); replacement of ->follow_link().  The differences
are:
	* inode and dentry are passed separately
	* might be called both in RCU and non-RCU mode;
the former is indicated by passing it a NULL dentry.
	* when called that way it isn't allowed to block
and should return ERR_PTR(-ECHILD) if it needs to be called
in non-RCU mode.

It's a flagday change - the old method is gone, all in-tree instances
converted.  Conversion isn't hard; said that, so far very few instances
do not immediately bail out when called in RCU mode.  That'll change
in the next commits.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 8 insertions, 4 deletions

diff --git a/mm/shmem.c b/mm/shmem.c
index 64bf5acb49fe..684dbc32e233 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -2496,10 +2496,14 @@ static int shmem_symlink(struct inode *dir, struct dentry *dentry, const char *s
         return 0;
 }
 
-static const char *shmem_follow_link(struct dentry *dentry, void **cookie)
+static const char *shmem_get_link(struct dentry *dentry,
+                                  struct inode *inode, void **cookie)
 {
         struct page *page = NULL;
-        int error = shmem_getpage(d_inode(dentry), 0, &page, SGP_READ, NULL);
+        int error;
+        if (!dentry)
+                return ERR_PTR(-ECHILD);
+        error = shmem_getpage(inode, 0, &page, SGP_READ, NULL);
         if (error)
                 return ERR_PTR(error);
         unlock_page(page);
@@ -2656,7 +2660,7 @@ static ssize_t shmem_listxattr(struct dentry *dentry, char *buffer, size_t size)
 
 static const struct inode_operations shmem_short_symlink_operations = {
         .readlink       = generic_readlink,
-        .follow_link    = simple_follow_link,
+        .get_link       = simple_get_link,
 #ifdef CONFIG_TMPFS_XATTR
         .setxattr       = shmem_setxattr,
         .getxattr       = shmem_getxattr,
@@ -2667,7 +2671,7 @@ static const struct inode_operations shmem_short_symlink_operations = {
 
 static const struct inode_operations shmem_symlink_inode_operations = {
         .readlink       = generic_readlink,
-        .follow_link    = shmem_follow_link,
+        .get_link       = shmem_get_link,
         .put_link       = shmem_put_link,
 #ifdef CONFIG_TMPFS_XATTR
         .setxattr       = shmem_setxattr,