On Wed, Nov 11, 2020 at 4:04 AM Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote:
>
> On Thu, Oct 08, 2020 at 03:53:51PM +0800, yulei.kernel@xxxxxxxxx wrote:
>
> > +static struct inode *
> > +dmemfs_get_inode(struct super_block *sb, const struct inode *dir, umode_t mode,
> > + dev_t dev);
>
> WTF is 'dev' for?
>
> > +static int
> > +dmemfs_mknod(struct inode *dir, struct dentry *dentry, umode_t mode, dev_t dev)
> > +{
> > + struct inode *inode = dmemfs_get_inode(dir->i_sb, dir, mode, dev);
> > + int error = -ENOSPC;
> > +
> > + if (inode) {
> > + d_instantiate(dentry, inode);
> > + dget(dentry); /* Extra count - pin the dentry in core */
> > + error = 0;
> > + dir->i_mtime = dir->i_ctime = current_time(inode);
> > + }
> > + return error;
> > +}
>
> ... same here, seeing that you only call that thing from the next two functions
> and you do *not* provide ->mknod() as a method (unsurprisingly - what would
> device nodes do there?)
>
Thanks for pointing this out. we may need support the mknod method, otherwise
the dev is redundant and need to be removed.
> > +static int dmemfs_create(struct inode *dir, struct dentry *dentry,
> > + umode_t mode, bool excl)
> > +{
> > + return dmemfs_mknod(dir, dentry, mode | S_IFREG, 0);
> > +}
> > +
> > +static int dmemfs_mkdir(struct inode *dir, struct dentry *dentry,
> > + umode_t mode)
> > +{
> > + int retval = dmemfs_mknod(dir, dentry, mode | S_IFDIR, 0);
> > +
> > + if (!retval)
> > + inc_nlink(dir);
> > + return retval;
> > +}
>
> > +int dmemfs_file_mmap(struct file *file, struct vm_area_struct *vma)
> > +{
> > + return 0;
> > +}
> > +
> > +static const struct file_operations dmemfs_file_operations = {
> > + .mmap = dmemfs_file_mmap,
> > +};
>
> Er... Is that a placeholder for later in the series? Because as it is,
> it makes no sense whatsoever - "it can be mmapped, but any access to the
> mapped area will segfault".
>
Yes, we seperate the full implementation for dmemfs_file_mmap into
patch 05/35, it
will assign the interfaces to handle the page fault.
> > +struct inode *dmemfs_get_inode(struct super_block *sb,
> > + const struct inode *dir, umode_t mode, dev_t dev)
> > +{
> > + struct inode *inode = new_inode(sb);
> > +
> > + if (inode) {
> > + inode->i_ino = get_next_ino();
> > + inode_init_owner(inode, dir, mode);
> > + inode->i_mapping->a_ops = &empty_aops;
> > + mapping_set_gfp_mask(inode->i_mapping, GFP_HIGHUSER);
> > + mapping_set_unevictable(inode->i_mapping);
> > + inode->i_atime = inode->i_mtime = inode->i_ctime = current_time(inode);
> > + switch (mode & S_IFMT) {
> > + default:
> > + init_special_inode(inode, mode, dev);
> > + break;
> > + case S_IFREG:
> > + inode->i_op = &dmemfs_file_inode_operations;
> > + inode->i_fop = &dmemfs_file_operations;
> > + break;
> > + case S_IFDIR:
> > + inode->i_op = &dmemfs_dir_inode_operations;
> > + inode->i_fop = &simple_dir_operations;
> > +
> > + /*
> > + * directory inodes start off with i_nlink == 2
> > + * (for "." entry)
> > + */
> > + inc_nlink(inode);
> > + break;
> > + case S_IFLNK:
> > + inode->i_op = &page_symlink_inode_operations;
> > + break;
>
> Where would symlinks come from? Or anything other than regular files and
> directories, for that matter...
You are right, so far it just supports regular files and directories.
