Re: [patch] eventfd - revised interface and cleanups

Randy Dunlap
2009-06-23T17:01:24Z

Davide Libenzi wrote:
> The following patch changes the eventfd interface to de-couple the eventfd
> memory context, from the file pointer instance.
> Without such change, there is no clean way to racely free handle the
> POLLHUP event sent when the last instance of the file* goes away.
> Also, now the internal eventfd APIs are using the eventfd context instead
> of the file*.
> Another cleanup this patch does, is making AIO select EVENTFD, instead of
> adding a bunch of empty function stubs inside eventfd.h.
>
> Andrew, this better go via Avi and the KVM tree, since they have patches
> that will be based on the new interface.
>
>
>
> Signed-off-by: Davide Libenzi <davidel@xmailserver.org>
>
>
> - Davide
>
>
> ---
> drivers/lguest/lg.h | 2
> drivers/lguest/lguest_user.c | 4 -
> fs/aio.c | 24 ++--------
> fs/eventfd.c | 101 ++++++++++++++++++++++++++++++++++++++-----
> include/linux/aio.h | 4 -
> include/linux/eventfd.h | 17 ++-----
> init/Kconfig | 1
> 7 files changed, 108 insertions(+), 45 deletions(-)
>
> Index: linux-2.6.mod/fs/eventfd.c
> ===================================================================
> --- linux-2.6.mod.orig/fs/eventfd.c 2009-06-21 16:54:15.000000000 -0700
> +++ linux-2.6.mod/fs/eventfd.c 2009-06-23 09:34:42.000000000 -0700
> @@ -17,32 +17,38 @@

> -/*
> - * Adds "n" to the eventfd counter "count". Returns "n" in case of
> - * success, or a value lower then "n" in case of coutner overflow.
> - * This function is supposed to be called by the kernel in paths
> - * that do not allow sleeping. In this function we allow the counter
> - * to reach the ULLONG_MAX value, and we signal this as overflow
> - * condition by returining a POLLERR to poll(2).
> +/**
> + * eventfd_signal - Adds @n to the eventfd counter. This function is
> + * supposed to be called by the kernel in paths that do not
> + * allow sleeping. In this function we allow the counter
> + * to reach the ULLONG_MAX value, and we signal this as
> + * overflow condition by returining a POLLERR to poll(2).
> + *

kernel-doc syntax requires the function name + short description on one line,
followed by parameters. Any longer function description then comes after
the parameters.

See Documentation/kernel-doc-nano-HOWTO.txt for more info,
or ask me.

> + * @ctx: [in] Pointer to the eventfd context.
> + * @n: [in] Value of the counter to be added to the eventfd internal counter.
> + *
> + * Returns: In case of success, it returns @n, otherwise (in case of overflow
> + * of the eventfd 64bit internal counter) a value lower than @n.
> */
> -int eventfd_signal(struct file *file, int n)
> +int eventfd_signal(struct eventfd_ctx *ctx, int n)
> {
> - struct eventfd_ctx *ctx = file->private_data;
> unsigned long flags;
>
> if (n < 0)

> +/**
> + * eventfd_ctx_put - Releases a reference to the internal eventfd context
> + * (previously acquired either with eventfd_ctx_get() or
> + * eventfd_ctx_fdget()).
> + *
> + * @ctx: [in] Pointer to eventfd context.
> + *
> + * Returns: Nothing.
> + */
> +void eventfd_ctx_put(struct eventfd_ctx *ctx)
> +{
> + kref_put(&ctx->kref, eventfd_free);
> +}
> +EXPORT_SYMBOL_GPL(eventfd_ctx_put);
> +
> static int eventfd_release(struct inode *inode, struct file *file)
> {
> - kfree(file->private_data);
> + struct eventfd_ctx *ctx = file->private_data;
> +
> + wake_up_poll(&ctx->wqh, POLLHUP);
> + eventfd_ctx_put(ctx);
> return 0;
> }

>
> +/**
> + * eventfd_ctx_fdget - Acquires a reference to the internal eventfd context
> + * given an eventfd file descriptor.
> + *
> + * @fd: [in] Eventfd file descriptor.
> + *
> + * Returns: In case of success, it returns a pointer to the internal eventfd
> + * context, otherwise a proper error code.
> + */
> +struct eventfd_ctx *eventfd_ctx_fdget(int fd)
> +{
> + struct file *file;
> + struct eventfd_ctx *ctx;
> +
> + file = eventfd_fget(fd);
> + if (IS_ERR(file))
> + return (struct eventfd_ctx *) file;
> + ctx = eventfd_ctx_get(file->private_data);
> + fput(file);
> +
> + return ctx;
> +}
> +EXPORT_SYMBOL_GPL(eventfd_ctx_fdget);

--
~Randy
LPC 2009, Sept. 23-25, Portland, Oregon