From 64d608db38ffc0c7a25455387096e0aad9410397 Mon Sep 17 00:00:00 2001 From: Jiri Slaby Date: Wed, 5 May 2021 11:19:06 +0200 Subject: tty: cumulate and document tty_struct::ctrl* members Group the ctrl members under a single struct called ctrl. The new struct contains 'pgrp', 'session', 'pktstatus', and 'packet'. 'pktstatus' and 'packet' used to be bits in a bitfield. The struct also contains the lock protecting them to 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::ctrl_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. Add a kerneldoc comment for this grouped members. Signed-off-by: Jiri Slaby Cc: "David S. Miller" Cc: Jakub Kicinski Cc: netdev@vger.kernel.org Link: https://lore.kernel.org/r/20210505091928.22010-14-jslaby@suse.cz Signed-off-by: Greg Kroah-Hartman --- include/linux/tty.h | 26 ++++++++++++++++---------- 1 file changed, 16 insertions(+), 10 deletions(-) (limited to 'include/linux/tty.h') diff --git a/include/linux/tty.h b/include/linux/tty.h index df3a69b2e1ea..283ac5f29052 100644 --- a/include/linux/tty.h +++ b/include/linux/tty.h @@ -255,6 +255,13 @@ struct tty_operations; * @flow.unused: alignment for Alpha, so that no members other than @flow.* are * modified by the same 64b word store. The @flow's __aligned is * there for the very same reason. + * @ctrl.lock: lock for ctrl members + * @ctrl.pgrp: process group of this tty (setpgrp(2)) + * @ctrl.session: session of this tty (setsid(2)). Writes are protected by both + * @ctrl.lock and legacy mutex, readers must use at least one of + * them. + * @ctrl.pktstatus: packet mode status (bitwise OR of TIOCPKT_* constants) + * @ctrl.packet: packet mode enabled * * All of the state associated with a tty while the tty is open. Persistent * storage for tty devices is referenced here as @port in struct tty_port. @@ -276,16 +283,9 @@ struct tty_struct { struct mutex throttle_mutex; struct rw_semaphore termios_rwsem; struct mutex winsize_mutex; - spinlock_t ctrl_lock; /* Termios values are protected by the termios rwsem */ struct ktermios termios, termios_locked; char name[64]; - struct pid *pgrp; /* Protected by ctrl lock */ - /* - * Writes protected by both ctrl lock and legacy mutex, readers must use - * at least one of them. - */ - struct pid *session; unsigned long flags; int count; struct winsize winsize; /* winsize_mutex */ @@ -297,10 +297,16 @@ struct tty_struct { unsigned long unused[0]; } __aligned(sizeof(unsigned long)) flow; + struct { + spinlock_t lock; + struct pid *pgrp; + struct pid *session; + unsigned char pktstatus; + bool packet; + unsigned long unused[0]; + } __aligned(sizeof(unsigned long)) ctrl; + int hw_stopped; - unsigned long ctrl_status:8, /* ctrl_lock */ - packet:1, - unused_ctrl:BITS_PER_LONG - 9; unsigned int receive_room; /* Bytes free for queue */ int flow_change; -- cgit