2020-05-01 17:57:01

by Jens Axboe

Subject: [PATCH v3] eventfd: convert to f_op->read_iter()

eventfd is using ->read() as it's file_operations read handler, but
this prevents passing in information about whether a given IO operation
is blocking or not. We can only use the file flags for that. To support
async (-EAGAIN/poll based) retries for io_uring, we need ->read_iter()
support. Convert eventfd to using ->read_iter().

Signed-off-by: Jens Axboe <[email protected]>

---

Since v2:

- Cleanup eventfd_read() as per Al's suggestions

Since v1:

- Add FMODE_NOWAIT to the eventfd file

diff --git a/fs/eventfd.c b/fs/eventfd.c
index 78e41c7c3d05..d590c2141d39 100644
--- a/fs/eventfd.c
+++ b/fs/eventfd.c
@@ -216,10 +216,11 @@ int eventfd_ctx_remove_wait_queue(struct eventfd_ctx *ctx, wait_queue_entry_t *w
}
EXPORT_SYMBOL_GPL(eventfd_ctx_remove_wait_queue);

-static ssize_t eventfd_read(struct file *file, char __user *buf, size_t count,
- loff_t *ppos)
+static ssize_t eventfd_read(struct kiocb *iocb, struct iov_iter *iov)
{
+ struct file *file = iocb->ki_filp;
struct eventfd_ctx *ctx = file->private_data;
+ size_t count = iov_iter_count(iov);
ssize_t res;
__u64 ucnt = 0;
DECLARE_WAITQUEUE(wait, current);
@@ -231,7 +232,8 @@ static ssize_t eventfd_read(struct file *file, char __user *buf, size_t count,
res = -EAGAIN;
if (ctx->count > 0)
res = sizeof(ucnt);
- else if (!(file->f_flags & O_NONBLOCK)) {
+ else if (!(file->f_flags & O_NONBLOCK) &&
+ !(iocb->ki_flags & IOCB_NOWAIT)) {
__add_wait_queue(&ctx->wqh, &wait);
for (;;) {
set_current_state(TASK_INTERRUPTIBLE);
@@ -257,7 +259,7 @@ static ssize_t eventfd_read(struct file *file, char __user *buf, size_t count,
}
spin_unlock_irq(&ctx->wqh.lock);

- if (res > 0 && put_user(ucnt, (__u64 __user *)buf))
+ if (res > 0 && copy_to_iter(&ucnt, res, iov) < res)
return -EFAULT;

return res;
@@ -329,7 +331,7 @@ static const struct file_operations eventfd_fops = {
#endif
.release = eventfd_release,
.poll = eventfd_poll,
- .read = eventfd_read,
+ .read_iter = eventfd_read,
.write = eventfd_write,
.llseek = noop_llseek,
};
@@ -427,8 +429,17 @@ static int do_eventfd(unsigned int count, int flags)

fd = anon_inode_getfd("[eventfd]", &eventfd_fops, ctx,
O_RDWR | (flags & EFD_SHARED_FCNTL_FLAGS));
- if (fd < 0)
+ if (fd < 0) {
eventfd_free_ctx(ctx);
+ } else {
+ struct file *file;
+
+ file = fget(fd);
+ if (file) {
+ file->f_mode |= FMODE_NOWAIT;
+ fput(file);
+ }
+ }

return fd;
}

--
Jens Axboe

2020-05-01 17:57:06

by Jens Axboe

Subject: Re: [PATCH v3] eventfd: convert to f_op->read_iter()

On 5/1/20 11:53 AM, Jens Axboe wrote:
> eventfd is using ->read() as it's file_operations read handler, but
> this prevents passing in information about whether a given IO operation
> is blocking or not. We can only use the file flags for that. To support
> async (-EAGAIN/poll based) retries for io_uring, we need ->read_iter()
> support. Convert eventfd to using ->read_iter().

Attached the wrong patch, forgot to update it... See 3b posting. I ran
this through my io_uring related eventfd testing, and it looks good.

--
Jens Axboe