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Slightly improve the design of the TTY buffer.

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The TTY buffers used the standard <sys/queue.h> lists. Unfortunately
they have a big shortcoming. If you want to have a double linked list,
but no tail pointer, it's still not possible to obtain the previous
element in the list. Inside the buffers we don't need them. This is why
I switched to custom linked list macros. The macros will also keep track
of the amount of items in the list. Because it doesn't use a sentinel,
we can just initialize the queues with zero.

In its simplest form (the output queue), we will only keep two
references to blocks in the queue, namely the head of the list and the
last block in use. All free blocks are stored behind the last block in
use.

I noticed there was a very subtle bug in the previous code: in a very
uncommon corner case, it would uma_zfree() a block in the queue before
calling memcpy() to extract the data from the block.
This commit is contained in:
Ed Schouten 2009-02-03 19:58:28 +00:00
parent e2f76cae05
commit 41ba7e9b13
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=188096
5 changed files with 121 additions and 107 deletions
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1
sys/dev/snp/snp.c
View File

@ -127,7 +127,6 @@ snp_open(struct cdev *dev, int flag, int mode, struct thread *td)
/* Allocate per-snoop data. */
ss = malloc(sizeof(struct snp_softc), M_SNP, M_WAITOK|M_ZERO);
ttyoutq_init(&ss->snp_outq);
cv_init(&ss->snp_outwait, "snp out");
devfs_set_cdevpriv(ss, snp_dtor);

3
sys/kern/tty.c
View File

@ -884,9 +884,6 @@ tty_alloc(struct ttydevsw *tsw, void *sc, struct mtx *mutex)
cv_init(&tp->t_bgwait, "ttybg");
cv_init(&tp->t_dcdwait, "ttydcd");
ttyinq_init(&tp->t_inq);
ttyoutq_init(&tp->t_outq);
/* Allow drivers to use a custom mutex to lock the TTY. */
if (mutex != NULL) {
tp->t_mtx = mutex;

78
sys/kern/tty_inq.c
View File

@ -79,13 +79,43 @@ SYSCTL_LONG(_kern, OID_AUTO, tty_inq_nslow, CTLFLAG_RD,
((tib)->tib_quotes[(boff) / BMSIZE] &= ~(1 << ((boff) % BMSIZE)))
struct ttyinq_block {
TAILQ_ENTRY(ttyinq_block) tib_list;
uint32_t tib_quotes[TTYINQ_QUOTESIZE];
char tib_data[TTYINQ_DATASIZE];
struct ttyinq_block *tib_prev;
struct ttyinq_block *tib_next;
uint32_t tib_quotes[TTYINQ_QUOTESIZE];
char tib_data[TTYINQ_DATASIZE];
};
static uma_zone_t ttyinq_zone;
#define TTYINQ_INSERT_TAIL(ti, tib) do { \
if (ti->ti_end == 0) { \
tib->tib_prev = NULL; \
tib->tib_next = ti->ti_firstblock; \
ti->ti_firstblock = tib; \
} else { \
tib->tib_prev = ti->ti_lastblock; \
tib->tib_next = ti->ti_lastblock->tib_next; \
ti->ti_lastblock->tib_next = tib; \
} \
if (tib->tib_next != NULL) \
tib->tib_next->tib_prev = tib; \
ti->ti_nblocks++; \
} while (0)
#define TTYINQ_REMOVE_HEAD(ti) do { \
ti->ti_firstblock = ti->ti_firstblock->tib_next; \
if (ti->ti_firstblock != NULL) \
ti->ti_firstblock->tib_prev = NULL; \
ti->ti_nblocks--; \
} while (0)
#define TTYINQ_RECYCLE(ti, tib) do { \
if (ti->ti_quota <= ti->ti_nblocks) \
uma_zfree(ttyinq_zone, tib); \
else \
TTYINQ_INSERT_TAIL(ti, tib); \
} while (0)
void
ttyinq_setsize(struct ttyinq *ti, struct tty *tp, size_t size)
{
@ -108,8 +138,7 @@ ttyinq_setsize(struct ttyinq *ti, struct tty *tp, size_t size)
tib = uma_zalloc(ttyinq_zone, M_WAITOK);
tty_lock(tp);
TAILQ_INSERT_TAIL(&ti->ti_list, tib, tib_list);
ti->ti_nblocks++;
TTYINQ_INSERT_TAIL(ti, tib);
}
}
@ -121,10 +150,9 @@ ttyinq_free(struct ttyinq *ti)
ttyinq_flush(ti);
ti->ti_quota = 0;
while ((tib = TAILQ_FIRST(&ti->ti_list)) != NULL) {
TAILQ_REMOVE(&ti->ti_list, tib, tib_list);
while ((tib = ti->ti_firstblock) != NULL) {
TTYINQ_REMOVE_HEAD(ti);
uma_zfree(ttyinq_zone, tib);
ti->ti_nblocks--;
}
MPASS(ti->ti_nblocks == 0);
@ -145,7 +173,7 @@ ttyinq_read_uio(struct ttyinq *ti, struct tty *tp, struct uio *uio,
/* See if there still is data. */
if (ti->ti_begin == ti->ti_linestart)
return (0);
tib = TAILQ_FIRST(&ti->ti_list);
tib = ti->ti_firstblock;
if (tib == NULL)
return (0);
@ -176,8 +204,7 @@ ttyinq_read_uio(struct ttyinq *ti, struct tty *tp, struct uio *uio,
* Fast path: zero copy. Remove the first block,
* so we can unlock the TTY temporarily.
*/
TAILQ_REMOVE(&ti->ti_list, tib, tib_list);
ti->ti_nblocks--;
TTYINQ_REMOVE_HEAD(ti);
ti->ti_begin = 0;
/*
@ -185,11 +212,10 @@ ttyinq_read_uio(struct ttyinq *ti, struct tty *tp, struct uio *uio,
* fix up the block offsets.
*/
#define CORRECT_BLOCK(t) do { \
if (t <= TTYINQ_DATASIZE) { \
if (t <= TTYINQ_DATASIZE) \
t = 0; \
} else { \
else \
t -= TTYINQ_DATASIZE; \
} \
} while (0)
CORRECT_BLOCK(ti->ti_linestart);
CORRECT_BLOCK(ti->ti_reprint);
@ -207,12 +233,7 @@ ttyinq_read_uio(struct ttyinq *ti, struct tty *tp, struct uio *uio,
tty_lock(tp);
/* Block can now be readded to the list. */
if (ti->ti_quota <= ti->ti_nblocks) {
uma_zfree(ttyinq_zone, tib);
} else {
TAILQ_INSERT_TAIL(&ti->ti_list, tib, tib_list);
ti->ti_nblocks++;
}
TTYINQ_RECYCLE(ti, tib);
} else {
char ob[TTYINQ_DATASIZE - 1];
atomic_add_long(&ttyinq_nslow, 1);
@ -264,25 +285,27 @@ ttyinq_write(struct ttyinq *ti, const void *buf, size_t nbytes, int quote)
size_t l;
while (nbytes > 0) {
tib = ti->ti_lastblock;
boff = ti->ti_end % TTYINQ_DATASIZE;
if (ti->ti_end == 0) {
/* First time we're being used or drained. */
MPASS(ti->ti_begin == 0);
tib = ti->ti_lastblock = TAILQ_FIRST(&ti->ti_list);
tib = ti->ti_firstblock;
if (tib == NULL) {
/* Queue has no blocks. */
break;
}
ti->ti_lastblock = tib;
} else if (boff == 0) {
/* We reached the end of this block on last write. */
tib = TAILQ_NEXT(tib, tib_list);
tib = ti->ti_lastblock->tib_next;
if (tib == NULL) {
/* We've reached the watermark. */
break;
}
ti->ti_lastblock = tib;
} else {
tib = ti->ti_lastblock;
}
/* Don't copy more than was requested. */
@ -328,7 +351,7 @@ size_t
ttyinq_findchar(struct ttyinq *ti, const char *breakc, size_t maxlen,
char *lastc)
{
struct ttyinq_block *tib = TAILQ_FIRST(&ti->ti_list);
struct ttyinq_block *tib = ti->ti_firstblock;
unsigned int boff = ti->ti_begin;
unsigned int bend = MIN(MIN(TTYINQ_DATASIZE, ti->ti_linestart),
ti->ti_begin + maxlen);
@ -402,8 +425,7 @@ ttyinq_unputchar(struct ttyinq *ti)
if (--ti->ti_end % TTYINQ_DATASIZE == 0) {
/* Roll back to the previous block. */
ti->ti_lastblock = TAILQ_PREV(ti->ti_lastblock,
ttyinq_bhead, tib_list);
ti->ti_lastblock = ti->ti_lastblock->tib_prev;
/*
* This can only fail if we are unputchar()'ing the
* first character in the queue.
@ -437,7 +459,7 @@ ttyinq_line_iterate(struct ttyinq *ti,
/* Use the proper block when we're at the queue head. */
if (offset == 0)
tib = TAILQ_FIRST(&ti->ti_list);
tib = ti->ti_firstblock;
/* Iterate all characters and call the iterator function. */
for (; offset < ti->ti_end; offset++) {
@ -449,7 +471,7 @@ ttyinq_line_iterate(struct ttyinq *ti,
/* Last byte iterated - go to the next block. */
if (boff == TTYINQ_DATASIZE - 1)
tib = TAILQ_NEXT(tib, tib_list);
tib = tib->tib_next;
MPASS(tib != NULL);
}
}

98
sys/kern/tty_outq.c
View File

@ -61,12 +61,35 @@ SYSCTL_LONG(_kern, OID_AUTO, tty_outq_nslow, CTLFLAG_RD,
&ttyoutq_nslow, 0, "Buffered reads to userspace on output");
struct ttyoutq_block {
STAILQ_ENTRY(ttyoutq_block) tob_list;
char tob_data[TTYOUTQ_DATASIZE];
struct ttyoutq_block *tob_next;
char tob_data[TTYOUTQ_DATASIZE];
};
static uma_zone_t ttyoutq_zone;
#define TTYOUTQ_INSERT_TAIL(to, tob) do { \
if (to->to_end == 0) { \
tob->tob_next = to->to_firstblock; \
to->to_firstblock = tob; \
} else { \
tob->tob_next = to->to_lastblock->tob_next; \
to->to_lastblock->tob_next = tob; \
} \
to->to_nblocks++; \
} while (0)
#define TTYOUTQ_REMOVE_HEAD(to) do { \
to->to_firstblock = to->to_firstblock->tob_next; \
to->to_nblocks--; \
} while (0)
#define TTYOUTQ_RECYCLE(to, tob) do { \
if (to->to_quota <= to->to_nblocks) \
uma_zfree(ttyoutq_zone, tob); \
else \
TTYOUTQ_INSERT_TAIL(to, tob); \
} while(0)
void
ttyoutq_flush(struct ttyoutq *to)
{
@ -97,8 +120,7 @@ ttyoutq_setsize(struct ttyoutq *to, struct tty *tp, size_t size)
tob = uma_zalloc(ttyoutq_zone, M_WAITOK);
tty_lock(tp);
STAILQ_INSERT_TAIL(&to->to_list, tob, tob_list);
to->to_nblocks++;
TTYOUTQ_INSERT_TAIL(to, tob);
}
}
@ -110,10 +132,9 @@ ttyoutq_free(struct ttyoutq *to)
ttyoutq_flush(to);
to->to_quota = 0;
while ((tob = STAILQ_FIRST(&to->to_list)) != NULL) {
STAILQ_REMOVE_HEAD(&to->to_list, tob_list);
while ((tob = to->to_firstblock) != NULL) {
TTYOUTQ_REMOVE_HEAD(to);
uma_zfree(ttyoutq_zone, tob);
to->to_nblocks--;
}
MPASS(to->to_nblocks == 0);
@ -131,7 +152,7 @@ ttyoutq_read(struct ttyoutq *to, void *buf, size_t len)
/* See if there still is data. */
if (to->to_begin == to->to_end)
break;
tob = STAILQ_FIRST(&to->to_list);
tob = to->to_firstblock;
if (tob == NULL)
break;
@ -146,30 +167,25 @@ ttyoutq_read(struct ttyoutq *to, void *buf, size_t len)
TTYOUTQ_DATASIZE);
clen = cend - cbegin;
if (cend == TTYOUTQ_DATASIZE || cend == to->to_end) {
/* Read the block until the end. */
STAILQ_REMOVE_HEAD(&to->to_list, tob_list);
if (to->to_quota < to->to_nblocks) {
uma_zfree(ttyoutq_zone, tob);
to->to_nblocks--;
} else {
STAILQ_INSERT_TAIL(&to->to_list, tob, tob_list);
}
to->to_begin = 0;
if (to->to_end <= TTYOUTQ_DATASIZE) {
to->to_end = 0;
} else {
to->to_end -= TTYOUTQ_DATASIZE;
}
} else {
/* Read the block partially. */
to->to_begin += clen;
}
/* Copy the data out of the buffers. */
memcpy(cbuf, tob->tob_data + cbegin, clen);
cbuf += clen;
len -= clen;
if (cend == to->to_end) {
/* Read the complete queue. */
to->to_begin = 0;
to->to_end = 0;
} else if (cend == TTYOUTQ_DATASIZE) {
/* Read the block until the end. */
TTYOUTQ_REMOVE_HEAD(to);
to->to_begin = 0;
to->to_end -= TTYOUTQ_DATASIZE;
TTYOUTQ_RECYCLE(to, tob);
} else {
/* Read the block partially. */
to->to_begin += clen;
}
}
return (cbuf - (char *)buf);
@ -197,7 +213,7 @@ ttyoutq_read_uio(struct ttyoutq *to, struct tty *tp, struct uio *uio)
/* See if there still is data. */
if (to->to_begin == to->to_end)
return (0);
tob = STAILQ_FIRST(&to->to_list);
tob = to->to_firstblock;
if (tob == NULL)
return (0);
@ -226,14 +242,12 @@ ttyoutq_read_uio(struct ttyoutq *to, struct tty *tp, struct uio *uio)
* Fast path: zero copy. Remove the first block,
* so we can unlock the TTY temporarily.
*/
STAILQ_REMOVE_HEAD(&to->to_list, tob_list);
to->to_nblocks--;
TTYOUTQ_REMOVE_HEAD(to);
to->to_begin = 0;
if (to->to_end <= TTYOUTQ_DATASIZE) {
if (to->to_end <= TTYOUTQ_DATASIZE)
to->to_end = 0;
} else {
else
to->to_end -= TTYOUTQ_DATASIZE;
}
/* Temporary unlock and copy the data to userspace. */
tty_unlock(tp);
@ -241,12 +255,7 @@ ttyoutq_read_uio(struct ttyoutq *to, struct tty *tp, struct uio *uio)
tty_lock(tp);
/* Block can now be readded to the list. */
if (to->to_quota <= to->to_nblocks) {
uma_zfree(ttyoutq_zone, tob);
} else {
STAILQ_INSERT_TAIL(&to->to_list, tob, tob_list);
to->to_nblocks++;
}
TTYOUTQ_RECYCLE(to, tob);
} else {
char ob[TTYOUTQ_DATASIZE - 1];
atomic_add_long(&ttyoutq_nslow, 1);
@ -280,26 +289,27 @@ ttyoutq_write(struct ttyoutq *to, const void *buf, size_t nbytes)
size_t l;
while (nbytes > 0) {
/* Offset in current block. */
tob = to->to_lastblock;
boff = to->to_end % TTYOUTQ_DATASIZE;
if (to->to_end == 0) {
/* First time we're being used or drained. */
MPASS(to->to_begin == 0);
tob = to->to_lastblock = STAILQ_FIRST(&to->to_list);
tob = to->to_firstblock;
if (tob == NULL) {
/* Queue has no blocks. */
break;
}
to->to_lastblock = tob;
} else if (boff == 0) {
/* We reached the end of this block on last write. */
tob = STAILQ_NEXT(tob, tob_list);
tob = to->to_lastblock->tob_next;
if (tob == NULL) {
/* We've reached the watermark. */
break;
}
to->to_lastblock = tob;
} else {
tob = to->to_lastblock;
}
/* Don't copy more than was requested. */

48
sys/sys/ttyqueue.h
View File

@ -43,29 +43,29 @@ struct uio;
/* Data input queue. */
struct ttyinq {
TAILQ_HEAD(ttyinq_bhead, ttyinq_block) ti_list;
struct ttyinq_block *ti_startblock;
struct ttyinq_block *ti_reprintblock;
struct ttyinq_block *ti_lastblock;
unsigned int ti_begin;
unsigned int ti_linestart;
unsigned int ti_reprint;
unsigned int ti_end;
unsigned int ti_nblocks;
unsigned int ti_quota;
struct ttyinq_block *ti_firstblock;
struct ttyinq_block *ti_startblock;
struct ttyinq_block *ti_reprintblock;
struct ttyinq_block *ti_lastblock;
unsigned int ti_begin;
unsigned int ti_linestart;
unsigned int ti_reprint;
unsigned int ti_end;
unsigned int ti_nblocks;
unsigned int ti_quota;
};
#define TTYINQ_DATASIZE 128
/* Data output queue. */
struct ttyoutq {
STAILQ_HEAD(, ttyoutq_block) to_list;
struct ttyoutq_block *to_lastblock;
unsigned int to_begin;
unsigned int to_end;
unsigned int to_nblocks;
unsigned int to_quota;
struct ttyoutq_block *to_firstblock;
struct ttyoutq_block *to_lastblock;
unsigned int to_begin;
unsigned int to_end;
unsigned int to_nblocks;
unsigned int to_quota;
};
#define TTYOUTQ_DATASIZE (256 - sizeof(STAILQ_ENTRY(ttyoutq_block)))
#define TTYOUTQ_DATASIZE (256 - sizeof(struct ttyoutq_block *))
#ifdef _KERNEL
/* Input queue handling routines. */
@ -86,13 +86,6 @@ void ttyinq_unputchar(struct ttyinq *ti);
void ttyinq_reprintpos_set(struct ttyinq *ti);
void ttyinq_reprintpos_reset(struct ttyinq *ti);
static __inline void
ttyinq_init(struct ttyinq *ti)
{
TAILQ_INIT(&ti->ti_list);
}
static __inline size_t
ttyinq_getsize(struct ttyinq *ti)
{
@ -143,13 +136,6 @@ int ttyoutq_read_uio(struct ttyoutq *to, struct tty *tp, struct uio *uio);
size_t ttyoutq_write(struct ttyoutq *to, const void *buf, size_t len);
int ttyoutq_write_nofrag(struct ttyoutq *to, const void *buf, size_t len);
static __inline void
ttyoutq_init(struct ttyoutq *to)
{
STAILQ_INIT(&to->to_list);
}
static __inline size_t
ttyoutq_getsize(struct ttyoutq *to)
{