Re: [PATCH v1 01/14] vfio: Create vfio_fs_type with inode per device

[Christoph Hellwig <hch@infradead.org>]

On Mon, Mar 08, 2021 at 02:47:28PM -0700, Alex Williamson wrote:
> By linking all the device fds we provide to userspace to an
> address space through a new pseudo fs, we can use tools like
> unmap_mapping_range() to zap all vmas associated with a device.
> 
> Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
> Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

I'd much prefer to just piggy back on the anon_inode fs rather than
duplicating this logic all over.  Something like the trivial patch below
should be all that is needed:

diff --git a/fs/anon_inodes.c b/fs/anon_inodes.c
index a280156138ed89..6fe404aab0f0dd 100644
--- a/fs/anon_inodes.c
+++ b/fs/anon_inodes.c
@@ -225,6 +225,12 @@ int anon_inode_getfd_secure(const char *name, const struct file_operations *fops
 }
 EXPORT_SYMBOL_GPL(anon_inode_getfd_secure);
 
+struct inode *alloc_anon_inode_simple(void)
+{
+	return alloc_anon_inode(anon_inode_mnt->mnt_sb);
+}
+EXPORT_SYMBOL_GPL(alloc_anon_inode_simple);
+
 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 71881a2b6f7860..6b2fb7d0abc57a 100644
--- a/include/linux/anon_inodes.h
+++ b/include/linux/anon_inodes.h
@@ -21,6 +21,7 @@ int anon_inode_getfd_secure(const char *name,
 			    const struct file_operations *fops,
 			    void *priv, int flags,
 			    const struct inode *context_inode);
+struct inode *alloc_anon_inode_simple(void);
 
 #endif /* _LINUX_ANON_INODES_H */