From mboxrd@z Thu Jan 1 00:00:00 1970 From: Greg Kroah-Hartman Date: Wed, 03 Jul 2019 17:11:55 +0000 Subject: Re: [PATCH 4/9] General notification queue with user mmap()'able ring buffer [ver #5] Message-Id: <20190703171155.GC24672@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit List-Id: References: <156173690158.15137.3985163001079120218.stgit@warthog.procyon.org.uk> <156173695061.15137.17196611619288074120.stgit@warthog.procyon.org.uk> In-Reply-To: <156173695061.15137.17196611619288074120.stgit@warthog.procyon.org.uk> To: David Howells Cc: viro@zeniv.linux.org.uk, Casey Schaufler , Stephen Smalley , nicolas.dichtel@6wind.com, raven@themaw.net, Christian Brauner , keyrings@vger.kernel.org, linux-usb@vger.kernel.org, linux-security-module@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-api@vger.kernel.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org On Fri, Jun 28, 2019 at 04:49:10PM +0100, David Howells wrote: > Implement a misc device that implements a general notification queue as a > ring buffer that can be mmap()'d from userspace. > > The way this is done is: > > (1) An application opens the device and indicates the size of the ring > buffer that it wants to reserve in pages (this can only be set once): > > fd = open("/dev/watch_queue", O_RDWR); > ioctl(fd, IOC_WATCH_QUEUE_NR_PAGES, nr_of_pages); > > (2) The application should then map the pages that the device has > reserved. Each instance of the device created by open() allocates > separate pages so that maps of different fds don't interfere with one > another. Multiple mmap() calls on the same fd, however, will all work > together. > > page_size = sysconf(_SC_PAGESIZE); > mapping_size = nr_of_pages * page_size; > char *buf = mmap(NULL, mapping_size, PROT_READ|PROT_WRITE, > MAP_SHARED, fd, 0); > > The ring is divided into 8-byte slots. Entries written into the ring are > variable size and can use between 1 and 63 slots. A special entry is > maintained in the first two slots of the ring that contains the head and > tail pointers. This is skipped when the ring wraps round. Note that > multislot entries, therefore, aren't allowed to be broken over the end of > the ring, but instead "skip" entries are inserted to pad out the buffer. > > Each entry has a 1-slot header that describes it: > > struct watch_notification { > __u32 type:24; > __u32 subtype:8; > __u32 info; > }; > > The type indicates the source (eg. mount tree changes, superblock events, > keyring changes, block layer events) and the subtype indicates the event > type (eg. mount, unmount; EIO, EDQUOT; link, unlink). The info field > indicates a number of things, including the entry length, an ID assigned to > a watchpoint contributing to this buffer, type-specific flags and meta > flags, such as an overrun indicator. > > Supplementary data, such as the key ID that generated an event, are > attached in additional slots. > > Signed-off-by: David Howells I don't know if I mentioned this before, but your naming seems a bit "backwards" from other subsystems. Should "watch_queue" always be the prefix, instead of a mix of prefix/suffix usage? Anyway, your call, it's your code :) Reviewed-by: Greg Kroah-Hartman From mboxrd@z Thu Jan 1 00:00:00 1970 From: Greg Kroah-Hartman Subject: Re: [PATCH 4/9] General notification queue with user mmap()'able ring buffer [ver #5] Date: Wed, 3 Jul 2019 19:11:55 +0200 Message-ID: <20190703171155.GC24672@kroah.com> References: <156173690158.15137.3985163001079120218.stgit@warthog.procyon.org.uk> <156173695061.15137.17196611619288074120.stgit@warthog.procyon.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <156173695061.15137.17196611619288074120.stgit@warthog.procyon.org.uk> Sender: linux-kernel-owner@vger.kernel.org To: David Howells Cc: viro@zeniv.linux.org.uk, Casey Schaufler , Stephen Smalley , nicolas.dichtel@6wind.com, raven@themaw.net, Christian Brauner , keyrings@vger.kernel.org, linux-usb@vger.kernel.org, linux-security-module@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-api@vger.kernel.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org List-Id: linux-api@vger.kernel.org On Fri, Jun 28, 2019 at 04:49:10PM +0100, David Howells wrote: > Implement a misc device that implements a general notification queue as a > ring buffer that can be mmap()'d from userspace. > > The way this is done is: > > (1) An application opens the device and indicates the size of the ring > buffer that it wants to reserve in pages (this can only be set once): > > fd = open("/dev/watch_queue", O_RDWR); > ioctl(fd, IOC_WATCH_QUEUE_NR_PAGES, nr_of_pages); > > (2) The application should then map the pages that the device has > reserved. Each instance of the device created by open() allocates > separate pages so that maps of different fds don't interfere with one > another. Multiple mmap() calls on the same fd, however, will all work > together. > > page_size = sysconf(_SC_PAGESIZE); > mapping_size = nr_of_pages * page_size; > char *buf = mmap(NULL, mapping_size, PROT_READ|PROT_WRITE, > MAP_SHARED, fd, 0); > > The ring is divided into 8-byte slots. Entries written into the ring are > variable size and can use between 1 and 63 slots. A special entry is > maintained in the first two slots of the ring that contains the head and > tail pointers. This is skipped when the ring wraps round. Note that > multislot entries, therefore, aren't allowed to be broken over the end of > the ring, but instead "skip" entries are inserted to pad out the buffer. > > Each entry has a 1-slot header that describes it: > > struct watch_notification { > __u32 type:24; > __u32 subtype:8; > __u32 info; > }; > > The type indicates the source (eg. mount tree changes, superblock events, > keyring changes, block layer events) and the subtype indicates the event > type (eg. mount, unmount; EIO, EDQUOT; link, unlink). The info field > indicates a number of things, including the entry length, an ID assigned to > a watchpoint contributing to this buffer, type-specific flags and meta > flags, such as an overrun indicator. > > Supplementary data, such as the key ID that generated an event, are > attached in additional slots. > > Signed-off-by: David Howells I don't know if I mentioned this before, but your naming seems a bit "backwards" from other subsystems. Should "watch_queue" always be the prefix, instead of a mix of prefix/suffix usage? Anyway, your call, it's your code :) Reviewed-by: Greg Kroah-Hartman