[PATCH] anonfd: Make file read-only if fops->write is not set

[Roland Dreier <rdreier@cisco.com>]

It seems a couple places such as arch/ia64/kernel/perfmon.c and
drivers/infiniband/core/uverbs_main.c could use anon_inode_getfile()
instead of a private pseudo-fs + alloc_file(), if only there were a way
to get a read-only file.  So provide this by having anon_inode_getfile()
create a read-only file if the fops->write passed in is NULL.

Signed-off-by: Roland Dreier <rolandd@cisco.com>
---
Hi Davide,

Would you consider a patch like this?  I'm not sure if this is the most
elegant way to handle this -- perhaps extending the flags parameter to
say whether we want writable or not would be better.  Let me know if you
would prefer that.

Thanks,
  Roland

 fs/anon_inodes.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/anon_inodes.c b/fs/anon_inodes.c
index 2c99459..097f91f 100644
--- a/fs/anon_inodes.c
+++ b/fs/anon_inodes.c
@@ -121,13 +121,13 @@ struct file *anon_inode_getfile(const char *name,
 	d_instantiate(path.dentry, anon_inode_inode);
 
 	error = -ENFILE;
-	file = alloc_file(&path, FMODE_READ | FMODE_WRITE, fops);
+	file = alloc_file(&path, FMODE_READ | (fops->write ? FMODE_WRITE : 0), fops);
 	if (!file)
 		goto err_dput;
 	file->f_mapping = anon_inode_inode->i_mapping;
 
 	file->f_pos = 0;
-	file->f_flags = O_RDWR | (flags & O_NONBLOCK);
+	file->f_flags = (fops->write ? O_RDWR : O_RDONLY) | (flags & O_NONBLOCK);
 	file->f_version = 0;
 	file->private_data = priv;