Re: [FiST] a problem with dget

[Jerome de Vivie <jerome.devivie@free.fr>]

Nir Tzachar wrote:
> 
> hello all.
> 
> i encountered a strange problem, involving the reference count of
> dentries.
> 
> first, let me describe my file system (i'll be brief.. ):
> im implementing a file system which is supposed to emulate an object
> storage device. i use a wrapper like file system (much like wrapfs,
> and actually based on it) to store files on an underlying f/s as objects.
> 
> i hope someone can help me, i've been tackling this problem for more than
> a week: when i create a file(say "tmp"), all is fine.
> the problem arises when i umount and then remount the file system.
> after im done with lookup (inode->i_op->lookup), dentry->d_count.counter
> ==1, as should be. but, when i enter the unlink function
> (inode->i_op->unlink ) its dentry->d_count.counter == 0 . why is that?
> nowhere in the vfs code does anyone decreases the counter b4
> inode->i_op->unlink is called . am i right?

This counter should at least be at 1. You should do a dget before each
lower level call and a dput after (in case the dentry is freed by
another process when you are inside unlink). Tracking usage count is not
easy, you can try this macro inside "lookup" and "d_release":

#if 1 /* for debugging dget/dput */
#define dcount(x) printk("(%s):%i  at %s:%i\n",(x)->d_name.name,
atomic_read(&(x)->d_count), __FILE__, __LINE__)
#else
#define dcount(x)
#endif

Try also to unmount the lower level fs. If there are pending dentries,
you will see this message:
"VFS: Busy inodes after unmount. Self-destruct in 5 seconds.  Have a
nice day..."

regards,

j.

-- 
Jérôme de Vivie
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