Hi,
On Thu, Feb 13, 2014 at 12:14 PM, Abhijit Chandrakant Pawar < [email protected]> wrote: > Hi, > > On Thursday 13 February 2014 07:40 AM, freeman wrote: > > Hi list, > > > > I am a newbie in linux kernel programming. Recently I got stuck in a > > problem when doing > > practice in file system programming. I hope this list is the right place > > I can turn to. > > > > I want to replace some file operations of files in a certain > > directory,so that data can be > > decrypted/encrypted through read/write system call. So I: > > > > #1: Find the directory inode, save its original inode operation > > table,then replace > > the table: > > > > kern_path(pathname, LOOKUP_FOLLOW, &target_dir_path); > > lower_iops = target_dir_path.dentry->d_inode->i_op; > > target_dir_path.dentry->d_inode->i_op = &my_iops; > > > I assume that you are writing your own stackable filesystem. > Take a look at WRAPFS[1] and ecryptfs[2]. As a matter of fact, ecryptfs > does what you are expecting. > > To do this, you need to set your superblock operations for the lower > directory inode so the VFS use your filesystem instead of the original > filesystem. > Important steps to look are: > 1. get lower superblock from the lower directory inode > 2. assign this superblock as an overlay for your own superblock. > 3. Set your own superblock operations for the new superblock > 4. get a root inode for your superblock using the lower directory inode > 5. While you are getting the inode, you can set the file operations on > this inode which will help you achieve your case. > > The point to note that you need to interpose the inodes with VFS so that > everything would be routed to your filesystem. > > -- > Abhijit. > [1]http://wrapfs.filesystems.org/ > [2]http://ecryptfs.org/ > > > > #2: In my_iops, I mainly changed ".lookup" function like this to achive > > my goal －－ > > replace the file operation table of all files in the directory. > > > > static struct dentry *my_inode_lookup(struct inode *dir, struct dentry > > *dentry, > > struct nameidata *nd) > > { > > struct dentry *ret_dentry; > > > > ret_dentry = lower_iops->lookup(dir,dentry,nd); > > if (!ret_dentry) > > goto out; > > ret_dentry->d_inode->i_fop = &my_fops; > > out: > > return ret_dentry; > > } > > > > Things turns out that replacement of inode operation table of directory > > is successful > > but the changes in file operations are not functional: system works as > > it used to, > > totally ignore my_fops! > > > > I have no idea how to fix it. Can anybody help? > > Thanks for your attention! > > Regards > > > > Freeman Zhang > > > > > > _______________________________________________ > > Kernelnewbies mailing list > > [email protected] > > http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies > > > > _______________________________________________ > Kernelnewbies mailing list > [email protected] > http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies > Freeman - What you are doing seems to be correct - you may have missed some pointer some where. Which file system are you using, are you writing a layer on an existing file system or changing the code of a file system Try adding some debug messages whenever you change the operations which prints the dentry->name of the file, you will get an idea that the correct file's operations are getting modified. -- Regards, Rishi Agrawal
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