From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: David Howells <dhowells@redhat.com>
Cc: viro@zeniv.linux.org.uk, Casey Schaufler <casey@schaufler-ca.com>,
Stephen Smalley <sds@tycho.nsa.gov>,
nicolas.dichtel@6wind.com, raven@themaw.net,
Christian Brauner <christian@brauner.io>,
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
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 [thread overview]
Message-ID: <20190703171155.GC24672@kroah.com> (raw)
In-Reply-To: <156173695061.15137.17196611619288074120.stgit@warthog.procyon.org.uk>
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 <dhowells@redhat.com>
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 <gregkh@linuxfoundation.org>
next prev parent reply other threads:[~2019-07-03 17:12 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-28 15:48 [PATCH 0/9] Keyrings, Block and USB notifications [ver #5] David Howells
2019-06-28 15:48 ` [PATCH 1/9] uapi: General notification ring definitions " David Howells
2019-07-03 17:08 ` Greg Kroah-Hartman
2019-06-28 15:48 ` [PATCH 2/9] security: Add hooks to rule on setting a watch " David Howells
2019-07-08 18:46 ` Stephen Smalley
2019-06-28 15:49 ` [PATCH 3/9] security: Add a hook for the point of notification insertion " David Howells
2019-07-08 19:13 ` Stephen Smalley
2019-06-28 15:49 ` [PATCH 4/9] General notification queue with user mmap()'able ring buffer " David Howells
2019-07-03 17:11 ` Greg Kroah-Hartman [this message]
2019-06-28 15:49 ` [PATCH 5/9] keys: Add a notification facility " David Howells
2019-06-28 15:49 ` [PATCH 6/9] Add a general, global device notification watch list " David Howells
2019-07-03 17:16 ` Greg Kroah-Hartman
2019-07-03 19:08 ` Greg Kroah-Hartman
2019-07-04 16:04 ` David Howells
2019-07-05 5:17 ` Greg Kroah-Hartman
2019-07-05 8:04 ` David Howells
2019-07-05 8:44 ` Greg Kroah-Hartman
2019-07-05 14:40 ` Alan Stern
2019-06-28 15:49 ` [PATCH 7/9] block: Add block layer notifications " David Howells
2019-06-28 15:49 ` [PATCH 8/9] usb: Add USB subsystem " David Howells
2019-07-03 17:07 ` Greg Kroah-Hartman
2019-06-28 15:49 ` [PATCH 9/9] Add sample notification program " David Howells
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20190703171155.GC24672@kroah.com \
--to=gregkh@linuxfoundation.org \
--cc=casey@schaufler-ca.com \
--cc=christian@brauner.io \
--cc=dhowells@redhat.com \
--cc=keyrings@vger.kernel.org \
--cc=linux-api@vger.kernel.org \
--cc=linux-block@vger.kernel.org \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-security-module@vger.kernel.org \
--cc=linux-usb@vger.kernel.org \
--cc=nicolas.dichtel@6wind.com \
--cc=raven@themaw.net \
--cc=sds@tycho.nsa.gov \
--cc=viro@zeniv.linux.org.uk \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).