Re: [patch] eventfd - revised interface and cleanups (2nd rev)

Davide Libenzi
2009-06-23T21:55:06Z

On Tue, 23 Jun 2009, Andrew Morton wrote:

> On Tue, 23 Jun 2009 14:34:50 -0700 (PDT)
> Davide Libenzi <davidel@xmailserver.org> wrote:
>
> > On Tue, 23 Jun 2009, Andrew Morton wrote:
> >
> > > > Should functions be describing all the returned error codes, ala man pages?
> > > >
> > >
> > > I think so.
> >
> > This becomes pretty painful when the function calls other functions, for
> > which just relays the error code.
> > Should we be just documenting the error codes introduced by the function
> > code, and say that the function returns errors A, B, C plus all the ones
> > returned by the called functions X, Y, Z?
> > If not, it becomes hell in maintaining the comments...
>
> Well. Don't worry about making rules. Taste and common sense apply. "Will
> it be useful to readers if I explicitly document the return value". If
> "yes" then document away. If "no" then don't.

Are you OK with the format in the patch below?

- Davide

---
drivers/lguest/lg.h | 2
drivers/lguest/lguest_user.c | 4 -
fs/aio.c | 24 ++------
fs/eventfd.c | 122 ++++++++++++++++++++++++++++++++++++++-----
include/linux/aio.h | 4 -
include/linux/eventfd.h | 18 ++----
init/Kconfig | 1
7 files changed, 129 insertions(+), 46 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 14:45:54.000000000 -0700
@@ -14,35 +14,44 @@
#include <linux/list.h>
#include <linux/spinlock.h>
#include <linux/anon_inodes.h>
-#include <linux/eventfd.h>
#include <linux/syscalls.h>
#include <linux/module.h>
+#include <linux/kref.h>
+#include <linux/eventfd.h>

struct eventfd_ctx {
+ struct kref kref;
wait_queue_head_t wqh;
/*
* Every time that a write(2) is performed on an eventfd, the
* value of the __u64 being written is added to "count" and a
* wakeup is performed on "wqh". A read(2) will return the "count"
* value to userspace, and will reset "count" to zero. The kernel
- * size eventfd_signal() also, adds to the "count" counter and
+ * side eventfd_signal() also, adds to the "count" counter and
* issue a wakeup.
*/
__u64 count;
unsigned int flags;
};

-/*
- * 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.
+ * @ctx: [in] Pointer to the eventfd context.
+ * @n: [in] Value of the counter to be added to the eventfd internal counter.
+ * The value cannot be negative.
+ *
+ * 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).
+ *
+ * Returns @n in case of success, a non-negative number lower than @n in case
+ * of overflow, or the following error codes:
+ *
+ * -EINVAL : The value of @n is negative.
*/
-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)
@@ -59,9 +68,45 @@ int eventfd_signal(struct file *file, in
}
EXPORT_SYMBOL_GPL(eventfd_signal);

+static void eventfd_free(struct kref *kref)
+{
+ struct eventfd_ctx *ctx = container_of(kref, struct eventfd_ctx, kref);
+
+ kfree(ctx);
+}
+
+/**
+ * eventfd_ctx_get - Acquires a reference to the internal eventfd context.
+ * @ctx: [in] Pointer to the eventfd context.
+ *
+ * Returns: In case of success, returns a pointer to the eventfd context.
+ */
+struct eventfd_ctx *eventfd_ctx_get(struct eventfd_ctx *ctx)
+{
+ kref_get(&ctx->kref);
+ return ctx;
+}
+EXPORT_SYMBOL_GPL(eventfd_ctx_get);
+
+/**
+ * eventfd_ctx_put - Releases a reference to the internal eventfd context.
+ * @ctx: [in] Pointer to eventfd context.
+ *
+ * The eventfd context reference must have been previously acquired either
+ * with eventfd_ctx_get() or eventfd_ctx_fdget()).
+ */
+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;
}

@@ -185,6 +230,16 @@ static const struct file_operations even
.write = eventfd_write,
};

+/**
+ * eventfd_fget - Acquire a reference of an eventfd file descriptor.
+ * @fd: [in] Eventfd file descriptor.
+ *
+ * Returns a pointer to the eventfd file structure in case of success, or the
+ * following error pointer:
+ *
+ * -EBADF : Invalid @fd file descriptor.
+ * -EINVAL : The @fd file descriptor is not an eventfd file.
+ */
struct file *eventfd_fget(int fd)
{
struct file *file;
@@ -201,6 +256,48 @@ struct file *eventfd_fget(int fd)
}
EXPORT_SYMBOL_GPL(eventfd_fget);

+/**
+ * eventfd_ctx_fdget - Acquires a reference to the internal eventfd context.
+ * @fd: [in] Eventfd file descriptor.
+ *
+ * Returns a pointer to the internal eventfd context, otherwise the error
+ * pointers returned by the following functions:
+ *
+ * eventfd_fget
+ */
+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);
+
+/**
+ * eventfd_ctx_fileget - Acquires a reference to the internal eventfd context.
+ * @file: [in] Eventfd file pointer.
+ *
+ * Returns a pointer to the internal eventfd context, otherwise the error
+ * pointer:
+ *
+ * -EINVAL : The @fd file descriptor is not an eventfd file.
+ */
+struct eventfd_ctx *eventfd_ctx_fileget(struct file *file)
+{
+ if (file->f_op != &eventfd_fops)
+ return ERR_PTR(-EINVAL);
+
+ return eventfd_ctx_get(file->private_data);
+}
+EXPORT_SYMBOL_GPL(eventfd_ctx_fileget);
+
SYSCALL_DEFINE2(eventfd2, unsigned int, count, int, flags)
{
int fd;
@@ -217,6 +314,7 @@ SYSCALL_DEFINE2(eventfd2, unsigned int,
if (!ctx)
return -ENOMEM;

+ kref_init(&ctx->kref);
init_waitqueue_head(&ctx->wqh);
ctx->count = count;
ctx->flags = flags;
Index: linux-2.6.mod/include/linux/eventfd.h
===================================================================
--- linux-2.6.mod.orig/include/linux/eventfd.h 2009-06-21 16:54:15.000000000 -0700
+++ linux-2.6.mod/include/linux/eventfd.h 2009-06-23 10:58:15.000000000 -0700
@@ -8,10 +8,8 @@
#ifndef _LINUX_EVENTFD_H
#define _LINUX_EVENTFD_H

-#ifdef CONFIG_EVENTFD
-
-/* For O_CLOEXEC and O_NONBLOCK */
#include <linux/fcntl.h>
+#include <linux/file.h>

/*
* CAREFUL: Check include/asm-generic/fcntl.h when defining
@@ -27,16 +25,12 @@
#define EFD_SHARED_FCNTL_FLAGS (O_CLOEXEC | O_NONBLOCK)
#define EFD_FLAGS_SET (EFD_SHARED_FCNTL_FLAGS | EFD_SEMAPHORE)

+struct eventfd_ctx *eventfd_ctx_get(struct eventfd_ctx *ctx);
+void eventfd_ctx_put(struct eventfd_ctx *ctx);
struct file *eventfd_fget(int fd);
-int eventfd_signal(struct file *file, int n);
-
-#else /* CONFIG_EVENTFD */
-
-#define eventfd_fget(fd) ERR_PTR(-ENOSYS)
-static inline int eventfd_signal(struct file *file, int n)
-{ return 0; }
-
-#endif /* CONFIG_EVENTFD */
+struct eventfd_ctx *eventfd_ctx_fdget(int fd);
+struct eventfd_ctx *eventfd_ctx_fileget(struct file *file);
+int eventfd_signal(struct eventfd_ctx *ctx, int n);

#endif /* _LINUX_EVENTFD_H */

Index: linux-2.6.mod/fs/aio.c
===================================================================
--- linux-2.6.mod.orig/fs/aio.c 2009-06-21 16:54:15.000000000 -0700
+++ linux-2.6.mod/fs/aio.c 2009-06-22 10:54:13.000000000 -0700
@@ -485,6 +485,8 @@ static inline void really_put_req(struct
{
assert_spin_locked(&ctx->ctx_lock);

+ if (req->ki_eventfd != NULL)
+ eventfd_ctx_put(req->ki_eventfd);
if (req->ki_dtor)
req->ki_dtor(req);
if (req->ki_iovec != &req->ki_inline_vec)
@@ -509,8 +511,6 @@ static void aio_fput_routine(struct work
/* Complete the fput(s) */
if (req->ki_filp != NULL)
__fput(req->ki_filp);
- if (req->ki_eventfd != NULL)
- __fput(req->ki_eventfd);

/* Link the iocb into the context's free list */
spin_lock_irq(&ctx->ctx_lock);
@@ -528,8 +528,6 @@ static void aio_fput_routine(struct work
*/
static int __aio_put_req(struct kioctx *ctx, struct kiocb *req)
{
- int schedule_putreq = 0;
-
dprintk(KERN_DEBUG "aio_put(%p): f_count=%ld\n",
req, atomic_long_read(&req->ki_filp->f_count));

@@ -549,24 +547,16 @@ static int __aio_put_req(struct kioctx *
* we would not be holding the last reference to the file*, so
* this function will be executed w/out any aio kthread wakeup.
*/
- if (unlikely(atomic_long_dec_and_test(&req->ki_filp->f_count)))
- schedule_putreq++;
- else
- req->ki_filp = NULL;
- if (req->ki_eventfd != NULL) {
- if (unlikely(atomic_long_dec_and_test(&req->ki_eventfd->f_count)))
- schedule_putreq++;
- else
- req->ki_eventfd = NULL;
- }
- if (unlikely(schedule_putreq)) {
+ if (unlikely(atomic_long_dec_and_test(&req->ki_filp->f_count))) {
get_ioctx(ctx);
spin_lock(&fput_lock);
list_add(&req->ki_list, &fput_head);
spin_unlock(&fput_lock);
queue_work(aio_wq, &fput_work);
- } else
+ } else {
+ req->ki_filp = NULL;
really_put_req(ctx, req);
+ }
return 1;
}

@@ -1622,7 +1612,7 @@ static int io_submit_one(struct kioctx *
* an eventfd() fd, and will be signaled for each completed
* event using the eventfd_signal() function.
*/
- req->ki_eventfd = eventfd_fget((int) iocb->aio_resfd);
+ req->ki_eventfd = eventfd_ctx_fdget((int) iocb->aio_resfd);
if (IS_ERR(req->ki_eventfd)) {
ret = PTR_ERR(req->ki_eventfd);
req->ki_eventfd = NULL;
Index: linux-2.6.mod/include/linux/aio.h
===================================================================
--- linux-2.6.mod.orig/include/linux/aio.h 2009-06-21 16:54:15.000000000 -0700
+++ linux-2.6.mod/include/linux/aio.h 2009-06-23 09:19:11.000000000 -0700
@@ -121,9 +121,9 @@ struct kiocb {

/*
* If the aio_resfd field of the userspace iocb is not zero,
- * this is the underlying file* to deliver event to.
+ * this is the underlying eventfd context to deliver events to.
*/
- struct file *ki_eventfd;
+ struct eventfd_ctx *ki_eventfd;
};

#define is_sync_kiocb(iocb) ((iocb)->ki_key == KIOCB_SYNC_KEY)
Index: linux-2.6.mod/init/Kconfig
===================================================================
--- linux-2.6.mod.orig/init/Kconfig 2009-06-21 16:54:15.000000000 -0700
+++ linux-2.6.mod/init/Kconfig 2009-06-22 10:54:13.000000000 -0700
@@ -925,6 +925,7 @@ config SHMEM

config AIO
bool "Enable AIO support" if EMBEDDED
+ select EVENTFD
default y
help
This option enables POSIX asynchronous I/O which may by used
Index: linux-2.6.mod/drivers/lguest/lg.h
===================================================================
--- linux-2.6.mod.orig/drivers/lguest/lg.h 2009-06-21 16:54:15.000000000 -0700
+++ linux-2.6.mod/drivers/lguest/lg.h 2009-06-23 08:55:34.000000000 -0700
@@ -82,7 +82,7 @@ struct lg_cpu {

struct lg_eventfd {
unsigned long addr;
- struct file *event;
+ struct eventfd_ctx *event;
};

struct lg_eventfd_map {
Index: linux-2.6.mod/drivers/lguest/lguest_user.c
===================================================================
--- linux-2.6.mod.orig/drivers/lguest/lguest_user.c 2009-06-21 16:54:15.000000000 -0700
+++ linux-2.6.mod/drivers/lguest/lguest_user.c 2009-06-22 10:54:13.000000000 -0700
@@ -50,7 +50,7 @@ static int add_eventfd(struct lguest *lg

/* Now append new entry. */
new->map[new->num].addr = addr;
- new->map[new->num].event = eventfd_fget(fd);
+ new->map[new->num].event = eventfd_ctx_fdget(fd);
if (IS_ERR(new->map[new->num].event)) {
kfree(new);
return PTR_ERR(new->map[new->num].event);
@@ -357,7 +357,7 @@ static int close(struct inode *inode, st

/* Release any eventfds they registered. */
for (i = 0; i < lg->eventfds->num; i++)
- fput(lg->eventfds->map[i].event);
+ eventfd_ctx_put(lg->eventfds->map[i].event);
kfree(lg->eventfds);

/* If lg->dead doesn't contain an error code it will be NULL or a