[RFC/PATCH] Generalize poll events from eventfd

[Damian Hobson-Garcia <dhobsong@igel.co.jp>]

Hello all,

eventfd is very useful for generating POLLIN/POLLOUT poll events from user
space but some applications may want to generate POLLPRI/POLLERR events as well.
This patch submission aims to generalize the events generated by an
eventfd. This is a resubmission of a patch from Feb 2013[1]. The original
discussion trailed off without any conclusion, but the original author
has recently confirmed[2] that this functionality is still useful, so I
volunteered to rebase and resubmit the patch for discussion.

I have rebased this patch onto v4.2-rc5 and modified the original patch to
not add an indentation level to the implementations of eventfd_{read,write,
poll}.  I hope these changes will make it easier to review. The description of
the efd_mask structure was also updated.

I have a few comments and questions, but I will add those separately as a
reply for open discussion.

[1] https://lkml.org/lkml/2013/2/18/147
[2] https://lkml.org/lkml/2015/7/9/153

Thank you,
Damian

Martin Sustrik (1):
  eventfd: implementation of EFD_MASK flag

 fs/eventfd.c                 | 91 ++++++++++++++++++++++++++++++++++++++------
 include/linux/eventfd.h      | 16 +-------
 include/uapi/linux/eventfd.h | 40 +++++++++++++++++++
 3 files changed, 121 insertions(+), 26 deletions(-)
 create mode 100644 include/uapi/linux/eventfd.h

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1.9.1