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Wong" To: Christoph Hellwig Cc: viro@zeniv.linux.org.uk, Avi Kivity , linux-aio@kvack.org, linux-fsdevel@vger.kernel.org, netdev@vger.kernel.org, linux-api@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 05/28] fs: introduce new ->get_poll_head and ->poll_mask methods Message-ID: <20180321162907.GG4807@magnolia> References: <20180321074032.14211-1-hch@lst.de> <20180321074032.14211-6-hch@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180321074032.14211-6-hch@lst.de> User-Agent: Mutt/1.5.24 (2015-08-30) X-Proofpoint-Virus-Version: vendor=nai engine=5900 definitions=8839 signatures=668695 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=0 malwarescore=0 phishscore=0 bulkscore=0 spamscore=0 mlxscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1711220000 definitions=main-1803200127 Sender: linux-api-owner@vger.kernel.org X-Mailing-List: linux-api@vger.kernel.org X-getmail-retrieved-from-mailbox: INBOX X-Mailing-List: linux-kernel@vger.kernel.org List-ID: On Wed, Mar 21, 2018 at 08:40:09AM +0100, Christoph Hellwig wrote: > ->get_poll_head returns the waitqueue that the poll operation is going > to sleep on. Note that this means we can only use a single waitqueue > for the poll, unlike some current drivers that use two waitqueues for > different events. But now that we have keyed wakeups and heavily use > those for poll there aren't that many good reason left to keep the > multiple waitqueues, and if there are any ->poll is still around, the > driver just won't support aio poll. > > Signed-off-by: Christoph Hellwig Looks ok, Reviewed-by: Darrick J. Wong --D > --- > Documentation/filesystems/Locking | 7 ++++++- > Documentation/filesystems/vfs.txt | 13 +++++++++++++ > fs/select.c | 28 ++++++++++++++++++++++++++++ > include/linux/fs.h | 2 ++ > include/linux/poll.h | 27 +++++++++++++++++++++++---- > 5 files changed, 72 insertions(+), 5 deletions(-) > > diff --git a/Documentation/filesystems/Locking b/Documentation/filesystems/Locking > index 220bba28f72b..6d227f9d7bd9 100644 > --- a/Documentation/filesystems/Locking > +++ b/Documentation/filesystems/Locking > @@ -440,6 +440,8 @@ prototypes: > ssize_t (*write_iter) (struct kiocb *, struct iov_iter *); > int (*iterate) (struct file *, struct dir_context *); > __poll_t (*poll) (struct file *, struct poll_table_struct *); > + struct wait_queue_head * (*get_poll_head)(struct file *, __poll_t); > + __poll_t (*poll_mask) (struct file *, __poll_t); > long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long); > long (*compat_ioctl) (struct file *, unsigned int, unsigned long); > int (*mmap) (struct file *, struct vm_area_struct *); > @@ -470,7 +472,7 @@ prototypes: > }; > > locking rules: > - All may block. > + All except for ->poll_mask may block. > > ->llseek() locking has moved from llseek to the individual llseek > implementations. If your fs is not using generic_file_llseek, you > @@ -498,6 +500,9 @@ in sys_read() and friends. > the lease within the individual filesystem to record the result of the > operation > > +->poll_mask can be called with or without the waitqueue lock for the waitqueue > +returned from ->get_poll_head. > + > --------------------------- dquot_operations ------------------------------- > prototypes: > int (*write_dquot) (struct dquot *); > diff --git a/Documentation/filesystems/vfs.txt b/Documentation/filesystems/vfs.txt > index f608180ad59d..50ee13563271 100644 > --- a/Documentation/filesystems/vfs.txt > +++ b/Documentation/filesystems/vfs.txt > @@ -857,6 +857,8 @@ struct file_operations { > ssize_t (*write_iter) (struct kiocb *, struct iov_iter *); > int (*iterate) (struct file *, struct dir_context *); > __poll_t (*poll) (struct file *, struct poll_table_struct *); > + struct wait_queue_head * (*get_poll_head)(struct file *, __poll_t); > + __poll_t (*poll_mask) (struct file *, __poll_t); > long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long); > long (*compat_ioctl) (struct file *, unsigned int, unsigned long); > int (*mmap) (struct file *, struct vm_area_struct *); > @@ -901,6 +903,17 @@ otherwise noted. > activity on this file and (optionally) go to sleep until there > is activity. Called by the select(2) and poll(2) system calls > > + get_poll_head: Returns the struct wait_queue_head that poll, select, > + epoll or aio poll should wait on in case this instance only has single > + waitqueue. Can return NULL to indicate polling is not supported, > + or a POLL* value using the POLL_TO_PTR helper in case a grave error > + occured and ->poll_mask shall not be called. > + > + poll_mask: return the mask of POLL* values describing the file descriptor > + state. Called either before going to sleep on the waitqueue returned by > + get_poll_head, or after it has been woken. If ->get_poll_head and > + ->poll_mask are implemented ->poll does not need to be implement. > + > unlocked_ioctl: called by the ioctl(2) system call. > > compat_ioctl: called by the ioctl(2) system call when 32 bit system calls > diff --git a/fs/select.c b/fs/select.c > index ba91103707ea..cc270d7f6192 100644 > --- a/fs/select.c > +++ b/fs/select.c > @@ -34,6 +34,34 @@ > > #include > > +__poll_t vfs_poll(struct file *file, struct poll_table_struct *pt) > +{ > + unsigned int events = poll_requested_events(pt); > + struct wait_queue_head *head; > + > + if (unlikely(!file_can_poll(file))) > + return DEFAULT_POLLMASK; > + > + if (file->f_op->poll) > + return file->f_op->poll(file, pt); > + > + /* > + * Only get the poll head and do the first mask check if we are actually > + * going to sleep on this file: > + */ > + if (pt && pt->_qproc) { > + head = vfs_get_poll_head(file, events); > + if (!head) > + return DEFAULT_POLLMASK; > + if (IS_ERR(head)) > + return PTR_TO_POLL(head); > + > + pt->_qproc(file, head, pt); > + } > + > + return file->f_op->poll_mask(file, events); > +} > +EXPORT_SYMBOL_GPL(vfs_poll); > > /* > * Estimate expected accuracy in ns from a timeval. > diff --git a/include/linux/fs.h b/include/linux/fs.h > index 79c413985305..6ea2c0843bb1 100644 > --- a/include/linux/fs.h > +++ b/include/linux/fs.h > @@ -1708,6 +1708,8 @@ struct file_operations { > int (*iterate) (struct file *, struct dir_context *); > int (*iterate_shared) (struct file *, struct dir_context *); > __poll_t (*poll) (struct file *, struct poll_table_struct *); > + struct wait_queue_head * (*get_poll_head)(struct file *, __poll_t); > + __poll_t (*poll_mask) (struct file *, __poll_t); > long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long); > long (*compat_ioctl) (struct file *, unsigned int, unsigned long); > int (*mmap) (struct file *, struct vm_area_struct *); > diff --git a/include/linux/poll.h b/include/linux/poll.h > index 7e0fdcf905d2..42e8e8665fb0 100644 > --- a/include/linux/poll.h > +++ b/include/linux/poll.h > @@ -74,18 +74,37 @@ static inline void init_poll_funcptr(poll_table *pt, poll_queue_proc qproc) > pt->_key = ~(__poll_t)0; /* all events enabled */ > } > > +/* > + * ->get_poll_head can return a __poll_t in the PTR_ERR, use these macros > + * to return the value and recover it. It takes care of the negation as > + * well as off the annotations. > + */ > +#define POLL_TO_PTR(mask) (ERR_PTR(-(__force int)(mask))) > +#define PTR_TO_POLL(ptr) ((__force __poll_t)-PTR_ERR((ptr))) > + > static inline bool file_can_poll(struct file *file) > { > - return file->f_op->poll; > + return file->f_op->poll || > + (file->f_op->get_poll_head && file->f_op->poll_mask); > } > > -static inline __poll_t vfs_poll(struct file *file, struct poll_table_struct *pt) > +static inline struct wait_queue_head *vfs_get_poll_head(struct file *file, > + __poll_t events) > { > - if (unlikely(!file->f_op->poll)) > + if (unlikely(!file->f_op->get_poll_head || !file->f_op->poll_mask)) > + return NULL; > + return file->f_op->get_poll_head(file, events); > +} > + > +static inline __poll_t vfs_poll_mask(struct file *file, __poll_t events) > +{ > + if (unlikely(!file->f_op->poll_mask)) > return DEFAULT_POLLMASK; > - return file->f_op->poll(file, pt); > + return file->f_op->poll_mask(file, events) & events; > } > > +__poll_t vfs_poll(struct file *file, struct poll_table_struct *pt); > + > struct poll_table_entry { > struct file *filp; > __poll_t key; > -- > 2.14.2 >