Re: [2.6.16 PATCH] Connector: Filesystem Events Connector

[Yi Yang <yang.y.yi@gmail.com>]

Evgeniy Polyakov wrote:
> On Wed, Mar 22, 2006 at 11:43:28PM -0800, Matt Helsley (matthltc@us.ibm.com) wrote:
>   
> > On Wed, 2006-03-22 at 22:58 +0800, Yi Yang wrote:
> >     
> > > This patch implements a new connector, Filesystem Event Connector,
> > >  the user can monitor filesystem activities via it, currently, it
> > >  can monitor access, attribute change, open, create, modify, delete,
> > >  move and close of any file or directory.
> > >
> > > Every filesystem event will include tgid, uid and gid of the process
> > >  which triggered this event, process name, file or directory name 
> > > operated by it.
> > >
> > > Filesystem events connector is never a duplicate of inotify, inotify
> > >  just concerns change on file or directory, Beagle uses it to watch
> > >  file changes in order to regenerate index for it, inotify can't tell
> > >  us who did that change and what is its process name, but filesystem
> > >  events connector can do these, moreover inotify's overhead is greater
> > >  than filesystem events connector, inotify needs compare inode with 
> > > watched file or directories list to decide whether it should generate an
> > >  inotify_event, some locks also increase overhead, filesystem event 
> > > connector hasn't these overhead, it just generates a fsevent and send.
> > >
> > > To be important, filesystem event connector doesn't add any new system 
> > > call, the user space application can make use of it by netlink socket, 
> > > but inotify added several system calls, many events mechanism in kernel
> > >  have used netlink as communication way with user space, for example, 
> > > KOBJECT_UEVENT, PROC_EVENTS, to use netlink will make it more possible
> > >  to unify events interface to netlink, the user space application can use 
> > > it very easy.
> > >
> > > Signed-off-by: Yi Yang <yang.y.yi@gmail.com>
> > >       
>
> Ugh, I like the idea!
>
>   
> > > --- a/include/linux/connector.h.orig	2006-03-15 23:21:37.000000000 +0800
> > > +++ b/include/linux/connector.h	2006-03-15 23:23:09.000000000 +0800
> > > @@ -34,6 +34,8 @@
> > >  #define CN_VAL_PROC			0x1
> > >  #define CN_IDX_CIFS			0x2
> > >  #define CN_VAL_CIFS                     0x1
> > > +#define CN_IDX_FS			0x3
> > > +#define CN_VAL_FS			0x1
> > >       
>
>
> Please add some on-line comment about what it is here.
>   
OK.
>   
> > >  #define CN_NETLINK_USERS		1
> > >       
>
>
> This must be increased each time new id is added.
> Although connector code does allocation with reserve, better to not
> exhaust it.
> Please increase it to 3.
>
> ...
>
>   
I'll do it.
> > > +/*
> > > + * Userspace sends this enum to register with the kernel that it is listening
> > > + * for events on the connector.
> > > + */
> > > +enum fsevent_mode {
> > > +	FSEVENT_LISTEN = 1,
> > > +	FSEVENT_IGNORE = 2
> > > +};
> > > +
> > >       
> > 	Process Events Connector uses this mechanism to avoid most of the event
> > generation code if there are no listeners. 
> >
> > 	Michael Kerrisk has privately suggested to me that this mechanism gives
> > userspace too much rope with which to hang itself. I think it just gives
> > userspace more rope.
> >
> > 	That said, perhaps we can shorten the rope by adding a connector
> > function to quickly return a value indicating if a process in userspace
> > is listening to messages sent by the kernel. Then connectors could use
> > that function rather that reinvent the same mechanism.
> >     
>
> Btw, current connector code performs check for listeners before it
> allocates any skbs.
> If there are no listenres -ESRCH is returned from cn_netlink_send().
>
> ...
>
>   
> > Pull the assignment out of the condition. You're not saving any space by
> > putting it into the if () and it's harder to read. I don't think the
> > __u8 cast is necessary..
> >
> >     
> > > +		printk("cn_fs: out of memory\n");
> > >       
> > missing printk tag
> >     
>
> Do not print such info at all.
>   
OK.
>   
> > > +void raise_fsevent(struct dentry * dentryp, u32 mask)
> > > +{
> > > +	__raise_fsevent(dentryp->d_name.name, NULL, mask);
> > > +}
> > > +EXPORT_SYMBOL_GPL(raise_fsevent);
> > > +
> > > +void raise_fsevent_create(struct inode * inode, const char * name, u32 mask)
> > > +{
> > > +	__raise_fsevent(name, NULL, mask);
> > > +}
> > > +EXPORT_SYMBOL_GPL(raise_fsevent_create);
> > > +
> > > +void raise_fsevent_move(struct inode * olddir, const char * oldname, 
> > > +		struct inode * newdir, const char * newname, u32 mask)
> > > +{
> > > +	__raise_fsevent(oldname, newname, mask);
> > > +}
> > > +EXPORT_SYMBOL_GPL(raise_fsevent_move);
> > >       
>
> Are there external modules which might use it?
>   
Yes, nfs will use it indirectly, because fsnotify is a common file 
system code path. if nfs is configured into module, compiler will complain
.

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