[1/4] fs/anon_inodes: new interface to create new inode

Commit Message

??? July 13, 2015, 8:35 a.m. UTC

From: Gioh Kim <[e-mail]>

The anon_inodes has already complete interfaces to create manage
many anonymous inodes but don't have interface to get
new inode. Other sub-modules can create anonymous inode
without creating and mounting it's own pseudo filesystem.

Signed-off-by: Gioh Kim <[e-mail]>
Acked-by: Rafael Aquini <[e-mail]>
---
 fs/anon_inodes.c            | 6 ++++++
 include/linux/anon_inodes.h | 1 +
 2 files changed, 7 insertions(+)

Comments

Mel Gorman July 29, 2015, 10:50 a.m. UTC | #1

On Mon, Jul 13, 2015 at 05:35:16PM +0900, Gioh Kim wrote:
> From: Gioh Kim <[e-mail]>
> 
> The anon_inodes has already complete interfaces to create manage
> many anonymous inodes but don't have interface to get
> new inode. Other sub-modules can create anonymous inode
> without creating and mounting it's own pseudo filesystem.
> 
> Signed-off-by: Gioh Kim <[e-mail]>
> Acked-by: Rafael Aquini <[e-mail]>

This is my first run through the series so I'm going to miss details but
this patch confuses me a little. You create an inode to associate with
the balloon dev_info so that page->mapping can be assigned. It's only the
mapping you care about for the aops so why are multiple inodes required? A
driver should be able to share and reference count a single inode. The
motivation to do it that way would be to reduce memory consumption and
this series is motivated by embedded platforms.

anon_inode_getfd has the following

 * Creates a new file by hooking it on a single inode. This is useful for files
 * that do not need to have a full-fledged inode in order to operate correctly.
 * All the files created with anon_inode_getfd() will share a single inode,
 * hence saving memory and avoiding code duplication for the file/inode/dentry
 * setup.  Returns new descriptor or an error code.

If all we care about the inode is the aops then it would follow that
anon_inode_getfd() is ideal. The tradeoff is reference counting overhead.
The changelog needs to explain why anon_inode_getfd() cannot be used.

Patch

diff --git a/fs/anon_inodes.c b/fs/anon_inodes.c
index 80ef38c..1d51f96 100644
--- a/fs/anon_inodes.c
+++ b/fs/anon_inodes.c
@@ -162,6 +162,12 @@  err_put_unused_fd:
 }
 EXPORT_SYMBOL_GPL(anon_inode_getfd);
 
+struct inode *anon_inode_new(void)
+{
+	return alloc_anon_inode(anon_inode_mnt->mnt_sb);
+}
+EXPORT_SYMBOL_GPL(anon_inode_new);
+
 static int __init anon_inode_init(void)
 {
 	anon_inode_mnt = kern_mount(&anon_inode_fs_type);
diff --git a/include/linux/anon_inodes.h b/include/linux/anon_inodes.h
index 8013a45..ddbd67f 100644
--- a/include/linux/anon_inodes.h
+++ b/include/linux/anon_inodes.h
@@ -15,6 +15,7 @@  struct file *anon_inode_getfile(const char *name,
 				void *priv, int flags);
 int anon_inode_getfd(const char *name, const struct file_operations *fops,
 		     void *priv, int flags);
+struct inode *anon_inode_new(void);
 
 #endif /* _LINUX_ANON_INODES_H */