Re: Help on automatic population of directories

[Maneesh Soni <maneesh@in.ibm.com>]

On Fri, Mar 05, 2004 at 04:57:49PM +0000, Shailabh wrote:
> Hi,
> 
> I'm writing a ram-based filesystem. I want the filesystem to 
> automatically create a few files inside every directory that a user creates.
> 
> 
> I'm trying to do this within the mkdir dir_inode op of the fs
> using code which looks like this:
> 
> >>>>>>>>>>>>>>>>>>
> /* rcfs_mknod and rcfs_get_inode are replicas of corresponding code from 
> fs/ramfs/inode.c */
> 
> static int
> rcfs_mknod(struct inode *dir, struct dentry *dentry, int mode, dev_t dev)
> {
> 	struct inode * inode = rcfs_get_inode(dir->i_sb, mode, dev);
> 	int error = -ENOSPC, i=0;
> 
> 	if (inode) {
> 		if (dir->i_mode & S_ISGID) {
> 			inode->i_gid = dir->i_gid;
> 			if (S_ISDIR(mode))
> 				inode->i_mode |= S_ISGID;
> 		}
> 		d_instantiate(dentry, inode);
> 		dget(dentry);	/* Extra count - pin the dentry in core */
> 		error = 0;
> 	}
> 	return error;
> }
> 
> static int rcfs_mkdir(struct inode * dir, struct dentry * dentry, int mode)
> {
> 	int retval = rcfs_mknod(dir, dentry, mode | S_IFDIR, 0);
> 	/* rcfs_mknod is a complete replica of 
> fs/ramfs/inode.c:ramfs_mknod */
> 
> 	if (!retval)
> 		dir->i_nlink++;
> 
> 	/* Do something here to create some "magic" files in this 
> directory before returning to the user */
> 
> 	return retval;
> }
> 
> <<<<<<<<<<<<<<<<<<<<<<<<<<
> 
> Q1: is there sufficient info in the dir/dentry variables  for a file to
> be created within rcfs_mkdir (at the comment point) ? If so, what would 
> be the best way to do this ?
> 

For creating new files, dentry and inode for the new files are needed. So
that can be done as follows where dentry is the dentry for the directory
under which you want to create new files.

	down(&dentry->d_inode->i_sem);
	new_dentry = rcfs_get_dentry(dentry->d_inode, "New_file");
	if (!IS_ERR(new_dentry)) {
		retval = rcfs_mknod(dentry->d_inode, new_dentry, mode, 0);
	}
	up(&dentry->d_inode->i_sem);

Now for rcfs_get_dentry(), have a look at sysfs_get_dentry(). This should
allocate new dentry if it is not already in dcache. Also you have to 
define ->lookup() dir_inode operation as simple_lookup().

> 
> Q2: How can one find the vfsmnt given the dentry of a directory that has
> just been created ?
> 
> I was thinking of using d_path() to lookup the complete path of the 
> just-created directory and then calling a modified version of sys_mknod
> on the resulting string. Probably not the best way of doing this but it 
> was simpler to understand :-) But I'm having trouble determining the 
> vfsmnt from the dentry returned from rcfs_mknod - I tried using
> current->namespace->root and also current->fs->rootmnt with no success -
> dpath returns blank or garbage as the resulting string and not 
> "/rcfs/hello/" which is what I expect when directory hello is being created.
> 

Why do you need this?..  It seems you want to know the absolute path for the
new created dentry. 

Maneesh

-- 
Maneesh Soni
Linux Technology Center, 
IBM Software Lab, Bangalore, India
email: maneesh@in.ibm.com
Phone: 91-80-25044999 Fax: 91-80-25268553
T/L : 9243696