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SubjectRe: [patch 3/8] procfs: Add ability to plug in auxiliary fdinfo providers
On Tue, Aug 14, 2012 at 06:03:45PM +0400, Cyrill Gorcunov wrote:
> This patch brings ability to plug in auxiliary fdinfo providers.
> For example in further patches eventfd, evenpoll and fsnotify
> will print out information associated with files.
>
> This feature is CONFIG_CHECKPOINT_RESTORE guarded to eliminate
> overhead for those who don't need it at all (this
> unfortunately makes patch bigger than I wanted).
>
> The basic usage rule is the following
>
> - fdinfo provider should register own "show" method
> via proc_register_fdinfo_driver call, where "show"
> methods are rather well known seq-file operations
>
> - once the kernel opens /proc/$pid/fdinfo/$fd file
> it calls for ->probe() method in registered fdinfo
> drivers, and if probe success, then seq-file "show"
> operations will be called to provide out additional
> infomation
>
> Initially we considered to inject some "show" metod to
> file_operations but since there really a number of
> file_operations declared inside kernel (and in real the
> further patches cover onle eventfd/epoll/inotify) the
> waste of memory space will be inacceptable I think.

NAK. This is too ugly to live. Put it into file_operations,
with NULL meaning default output, or don't do it at all.

And no, "it's only if you enable CONFIG_SOME_SHIT" gambit won't
fly - we have all seen it played too many times. All it takes
is one politically-inclined induhvidual adding a dependency to
some "vertically integrated" turd (*cough* systemd *spit* udev
*cough*) and we are stuck with the damn thing. CGROUP shite
is already there, DEVTMPFS is well on its way, etc.


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