anonfd: Allow making anon files read-only

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 we pass O_RDONLY in flags.

Signed-off-by: Roland Dreier <rolandd@cisco.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 10 insertions, 2 deletions

diff --git a/fs/anon_inodes.c b/fs/anon_inodes.c
index 2c994591f4d7..598237e97221 100644
--- a/fs/anon_inodes.c
+++ b/fs/anon_inodes.c
@@ -89,11 +89,19 @@ struct file *anon_inode_getfile(const char *name,
         struct qstr this;
         struct path path;
         struct file *file;
+        fmode_t mode;
         int error;
 
         if (IS_ERR(anon_inode_inode))
                 return ERR_PTR(-ENODEV);
 
+        switch (flags & O_ACCMODE) {
+        case O_RDONLY: mode = FMODE_READ;               break;
+        case O_WRONLY: mode = FMODE_WRITE;              break;
+        case O_RDWR:   mode = FMODE_READ | FMODE_WRITE; break;
+        default:       return ERR_PTR(-EINVAL);
+        }
+
         if (fops->owner && !try_module_get(fops->owner))
                 return ERR_PTR(-ENOENT);
 
@@ -121,13 +129,13 @@ 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, mode, 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 = flags & (O_ACCMODE | O_NONBLOCK);
         file->f_version = 0;
         file->private_data = priv;