Tracing VFS layer

[Prasanna S Panchamukhi <prasanna at in dot ibm dot com>]

Hi,

Tracing of VFS layer.

There are four interesting VFS objects, which most of the users 
would like to trace.
I have listed the VFS objects, filesystems, operations on specific vfs
objects below. Examples scripts are provided in the last section.

Your comments are welcome.

Thanks
Prasanna

1. Below are the list of VFS objects.
		<VFS objects> are : 	superblock
					inode
					file
					dentry
Few more VFS objects can be traced, such as struct file_system_type, and
struct vfsmount.

2. Below are the list of file systems present in linux 2.6 version

		<filesystem type> :	adfs
					affs
					afs
					autofs
					autofs4
					befs
					bfs
					cifs
					coda
					cramfs
					debugfs
					devfs
					devpts
					efs
					exportfs
					ext2
					ext3
					fat
					freevxfs
					hfs
					hfsplus
					hostfs
					hpfs
					hppfs
					hugetlbfs

3. Below are the list of operations on superblock object.
		<superblock operation>	:				
					alloc_inode
					destroy_inode
					read_inode
					dirty_inode
					write_inode
					put_inode
					drop_inode
					delete_inode
					put_super
					write_super
					sync_fs
					write_super_lockfs
					unlockfs
					statfs
					remount_fs
					clear_inode
					umount_begin
					show_options
					quota_read
					quota_write

4. Below are the list of operation on inode object.
		<inode operation> :
					create
					lookup
					link
					unlink
					symlink
					mkdir
					rmdir
					mknod
					rename
					readlink
					follow_link
					put_link
					truncate
					permission
					setattr
					getattr
					setxattr
					getxattr
					listxattr
					removexattr

5. Below are the list of operation on file object.
		<file operation>: 
					llseek
					read
					aio_read
					write
					aio_write
					readdir
					poll
					ioctl
					unlocked_ioctl
					compat_ioctl
					mmap
					open
					flush
					release
					fsync
					aio_fsync
					fasync
					lock
					readv
					writev
					sendfile
					sendpage
					get_unmapped_area
					check_flags
					dir_notify
					flock

6. Below are the list of operations on dentry object.
		<dentry operation>:
					d_revalidate
					d_hash
					d_compare
					d_delete
					d_release
					d_iput

7. Possible user options to trace the VFS layer

	1. User can write scripts to put probe on individual routine that acts
	   upon a particular object. For example if a user want to put probes
	   on all the routines that act on superblock and log some elements.

		 VFS:superblock:ext3:alloc_inode {
			
			trace(  "blocksize = ".	string($sb->s_blocksize),
				"s_dev= ".  	string($sb->s_dev),
				"s_type= ". 	string($sb->s_type)
			      );
		}
			
		VFS:superblock:ext3:write_super {

			trace(  "blocksize = ".	string($sb->s_blocksize),
				"s_dev= ".  	string($sb->s_dev),
				"s_type= ". 	string($sb->s_type)
			      );
		}

	In the example below user wants of put probes on the routines
	that act on dentry object and log some elements.	
	
		VFS:dentry:devfs:d_iput {

			trace(  "d_count= ".	string($dentry->d_count),
				"d_flag= ".  	string($dentry->d_flag)
			      );
		}

		VFS:dentry:devfs:d_release {

			trace(  "d_count= ".	string($dentry->d_count),
				"d_flag= ".  	string($dentry->d_flag)
			      );
		}
-- 

Prasanna S Panchamukhi
Linux Technology Center
India Software Labs, IBM Bangalore
Ph: 91-80-25044636
<prasanna@in.ibm.com>