diff options
| author |   Jiri Slaby <jslaby@suse.cz> | 2021-05-05 11:19:05 +0200 |
|---|---|---|
| committer |   Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2021-05-13 16:57:16 +0200 |
| commit | 6e94dbc7a4e49a028b81302d755bba1a518f973b (patch) | |
| tree | f96593e04f90e65cdca2110661b239cface50743 /include/linux/tty_driver.h | |
| parent | tty: make fp of tty_ldisc_ops::receive_buf{,2} const (diff) | |
| download | wireguard-linux-6e94dbc7a4e49a028b81302d755bba1a518f973b.tar.xz wireguard-linux-6e94dbc7a4e49a028b81302d755bba1a518f973b.zip | |
tty: cumulate and document tty_struct::flow* members
Group the flow flags under a single struct called flow. The new struct
contains 'stopped' and 'tco_stopped' bools which used to be bits in a
bitfield. The struct also contains the lock protecting them to
potentially share the same cache line.
Note that commit c545b66c6922b (tty: Serialize tcflow() with other tty
flow control changes) added a padding to the original bitfield. It was
for the bitfield to occupy a whole 64b word to avoid interferring stores
on Alpha (cannot we evaporate this arch with weird implications to C
code yet?). But it doesn't work as expected as the padding
(tty_struct::unused) is aligned to a 8B boundary too and occupies some
bytes from the next word.
So make it reliable by:
1) setting __aligned of the struct -- that aligns the start, and
2) making 'unsigned long unused[0]' as the last member of the struct --
pads the end.
This is also the perfect time to start the documentation of tty_struct
where all this lives. So we start by documenting what these bools
actually serve for. And why we do all the alignment dances. Only the few
up-to-date information from the Theodore's comment made it into this new
Kerneldoc comment.
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Ulf Hansson <ulf.hansson@linaro.org>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: Shawn Guo <shawnguo@kernel.org>
Cc: Sascha Hauer <s.hauer@pengutronix.de>
Cc: Vineet Gupta <vgupta@synopsys.com>
Cc: "Maciej W. Rozycki" <macro@orcam.me.uk>
Link: https://lore.kernel.org/r/20210505091928.22010-13-jslaby@suse.cz
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'include/linux/tty_driver.h')
| -rw-r--r-- | include/linux/tty_driver.h | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/include/linux/tty_driver.h b/include/linux/tty_driver.h index 2f719b471d52..653fa5af3a22 100644 --- a/include/linux/tty_driver.h +++ b/include/linux/tty_driver.h @@ -153,7 +153,7 @@ * This routine notifies the tty driver that it should stop * outputting characters to the tty device. * - * Called with ->flow_lock held. Serialized with start() method. + * Called with ->flow.lock held. Serialized with start() method. * * Optional: * @@ -164,7 +164,7 @@ * This routine notifies the tty driver that it resume sending * characters to the tty device. * - * Called with ->flow_lock held. Serialized with stop() method. + * Called with ->flow.lock held. Serialized with stop() method. * * Optional: * |