Aditya-
I'm not the best person to answer these questions, so I'm copying the
Kernel Newbies list. I'll try to answer as best as I can:
> 1.
> does dentry contains full path name ???
> ( for a path /user/bin/usr1 there will be 4 dentries and d_name.name
> will be "/", "/user" /user/bin", "/user/bin/usr1" )
> is this correct or the d_name.name will be "/", "user", "bin" and
> "usr1" and they will be linked by parent pointers. ??
Your second guess is correct. Each dentry holds the name of just its
component of the path ("/", "usr", "bin", "usr1"). Each dentry has a
parent pointer and a linked list of child pointers. The parent pointer
of the root dentry of a filesystem points at itself.
> 2.
> if both /home and /temp are both mountpoints for the /dev/hda5, and I
> have opened many files on /home/mbr .. but not on /temp
> .
> I am not able to unmount the /home because there are open files. but i
> can umount /temp.
>
> My question is how the VFS knows that there are open files at this
> particular mount point.
Because file structures point at both a dentry and a vfsmount structure.
Although the dentry tree is the same for both /home and /temp, each
mount has a separate vfsmount structure that points at the mountpoint's
dentry and vfsmount, as well as the root dentry of the mounted
filesystem. Because you're not using files under the /temp mountpoint,
its vfsmount structure is effectively unreferenced and can be unmounted.
Similarly, the current working directory and root directory information
for a task structure points at both dentries and vfsmounts.
> How VFS traverses back to system root, when same file system is
> mounted at various mount point.
Take a look at the __d_path() function in fs/dcache.c (around line 940).
It takes a dentry and vfsmount, then walks back the chain to build a
pathname. This is the function used when you do a `ls -l
/proc/<pid>/fds` to see what files a process has open.
Hope this helps,
Brian Watson
OpenSSI Clustering project
OpenSSI.org
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