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-rw-r--r--fs/readdir.c68
1 files changed, 52 insertions, 16 deletions
diff --git a/fs/readdir.c b/fs/readdir.c
index b264ce60114d..c8c46e294431 100644
--- a/fs/readdir.c
+++ b/fs/readdir.c
@@ -25,6 +25,53 @@
#include <asm/unaligned.h>
/*
+ * Some filesystems were never converted to '->iterate_shared()'
+ * and their directory iterators want the inode lock held for
+ * writing. This wrapper allows for converting from the shared
+ * semantics to the exclusive inode use.
+ */
+int wrap_directory_iterator(struct file *file,
+ struct dir_context *ctx,
+ int (*iter)(struct file *, struct dir_context *))
+{
+ struct inode *inode = file_inode(file);
+ int ret;
+
+ /*
+ * We'd love to have an 'inode_upgrade_trylock()' operation,
+ * see the comment in mmap_upgrade_trylock() in mm/memory.c.
+ *
+ * But considering this is for "filesystems that never got
+ * converted", it really doesn't matter.
+ *
+ * Also note that since we have to return with the lock held
+ * for reading, we can't use the "killable()" locking here,
+ * since we do need to get the lock even if we're dying.
+ *
+ * We could do the write part killably and then get the read
+ * lock unconditionally if it mattered, but see above on why
+ * this does the very simplistic conversion.
+ */
+ up_read(&inode->i_rwsem);
+ down_write(&inode->i_rwsem);
+
+ /*
+ * Since we dropped the inode lock, we should do the
+ * DEADDIR test again. See 'iterate_dir()' below.
+ *
+ * Note that we don't need to re-do the f_pos games,
+ * since the file must be locked wrt f_pos anyway.
+ */
+ ret = -ENOENT;
+ if (!IS_DEADDIR(inode))
+ ret = iter(file, ctx);
+
+ downgrade_write(&inode->i_rwsem);
+ return ret;
+}
+EXPORT_SYMBOL(wrap_directory_iterator);
+
+/*
* Note the "unsafe_put_user() semantics: we goto a
* label for errors.
*/
@@ -40,39 +87,28 @@
int iterate_dir(struct file *file, struct dir_context *ctx)
{
struct inode *inode = file_inode(file);
- bool shared = false;
int res = -ENOTDIR;
- if (file->f_op->iterate_shared)
- shared = true;
- else if (!file->f_op->iterate)
+
+ if (!file->f_op->iterate_shared)
goto out;
res = security_file_permission(file, MAY_READ);
if (res)
goto out;
- if (shared)
- res = down_read_killable(&inode->i_rwsem);
- else
- res = down_write_killable(&inode->i_rwsem);
+ res = down_read_killable(&inode->i_rwsem);
if (res)
goto out;
res = -ENOENT;
if (!IS_DEADDIR(inode)) {
ctx->pos = file->f_pos;
- if (shared)
- res = file->f_op->iterate_shared(file, ctx);
- else
- res = file->f_op->iterate(file, ctx);
+ res = file->f_op->iterate_shared(file, ctx);
file->f_pos = ctx->pos;
fsnotify_access(file);
file_accessed(file);
}
- if (shared)
- inode_unlock_shared(inode);
- else
- inode_unlock(inode);
+ inode_unlock_shared(inode);
out:
return res;
}