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open("/dev/ttyS1", O_LARGEFILE) blocks

DISCUSSION Bernd Petrovitsch 2 participants 4 messages Oct 14, 2002

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Bernd Petrovitsch

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#0 lore raw

Hi all!

Is is normal/correct/intended that an open() of /dev/ttyS1 blocks? ---- snip ----
{81}strace ./test-open /dev/ttyS0
[...]
open("/dev/ttyS0", O_RDONLY|O_NONBLOCK) = 3
close(3) = 0
open("/dev/ttyS0", O_RDONLY|O_NONBLOCK|O_LARGEFILE) = 3
close(3) = 0
open("/dev/ttyS0", O_RDONLY|O_LARGEFILE) = 3
close(3) = 0
_exit(0) = ?
{82}strace ./test-open /dev/ttyS1
[...]
open("/dev/ttyS1", O_RDONLY|O_NONBLOCK) = 3
close(3) = 0
open("/dev/ttyS1", O_RDONLY|O_NONBLOCK|O_LARGEFILE) = 3
close(3) = 0
open("/dev/ttyS1", O_RDONLY|O_LARGEFILE <unfinished ...> {83}lsof /dev/ttyS0
{84}lsof /dev/ttyS1
{85}uname -a
Linux xxx 2.4.20-pre10aa1 #6 Fri Oct 11 13:41:20 CEST 2002 i686 unknown ---- snip ----

The second one was terminated with a Ctrl-C.
Nothing was connected to none of the ports.
Is there a reason that an open() on /dev/ttyS0 works and blocks on /dev/ttyS1?

Bernd

Signature · 4 lines
Bernd Petrovitsch                              Email : [email protected]
g.a.m.s gmbh                                  Fax : +43 1 205255-900
Prinz-Eugen-Straße 8                    A-1040 Vienna/Austria/Europe
                     LUGA : http://www.luga.at
#1 lore raw
Quoted 26 lines · Bernd Petrovitsch

Hi all!

Is is normal/correct/intended that an open() of /dev/ttyS1 blocks? ---- snip ----
{81}strace ./test-open /dev/ttyS0
[...]
open("/dev/ttyS0", O_RDONLY|O_NONBLOCK) = 3
close(3) = 0
open("/dev/ttyS0", O_RDONLY|O_NONBLOCK|O_LARGEFILE) = 3
close(3) = 0
open("/dev/ttyS0", O_RDONLY|O_LARGEFILE) = 3
close(3) = 0
_exit(0) = ?
{82}strace ./test-open /dev/ttyS1
[...]
open("/dev/ttyS1", O_RDONLY|O_NONBLOCK) = 3
close(3) = 0
open("/dev/ttyS1", O_RDONLY|O_NONBLOCK|O_LARGEFILE) = 3
close(3) = 0
open("/dev/ttyS1", O_RDONLY|O_LARGEFILE <unfinished ...> {83}lsof /dev/ttyS0
{84}lsof /dev/ttyS1
{85}uname -a
Linux xxx 2.4.20-pre10aa1 #6 Fri Oct 11 13:41:20 CEST 2002 i686 unknown ---- snip ----

Quoted 4 lines

The second one was terminated with a Ctrl-C.
Nothing was connected to none of the ports.
Is there a reason that an open() on /dev/ttyS0 works and blocks on /dev/ttyS1?

stty -aF /dev/ttyS0
stty -aF /dev/ttyS1

I bet ttyS0 has clocal set, whereas ttyS1 doesn't.

Signature · 2 lines
Russell King ([email protected])                The developer of ARM Linux
             http://www.arm.linux.org.uk/personal/aboutme.html
author
#2 lore raw
Quoted 32 lines · Russell King
Quoted 26 lines · Bernd Petrovitsch

Hi all!

Is is normal/correct/intended that an open() of /dev/ttyS1 blocks? ---- snip ----
{81}strace ./test-open /dev/ttyS0
[...]
open("/dev/ttyS0", O_RDONLY|O_NONBLOCK) = 3
close(3) = 0
open("/dev/ttyS0", O_RDONLY|O_NONBLOCK|O_LARGEFILE) = 3
close(3) = 0
open("/dev/ttyS0", O_RDONLY|O_LARGEFILE) = 3
close(3) = 0
_exit(0) = ?
{82}strace ./test-open /dev/ttyS1
[...]
open("/dev/ttyS1", O_RDONLY|O_NONBLOCK) = 3
close(3) = 0
open("/dev/ttyS1", O_RDONLY|O_NONBLOCK|O_LARGEFILE) = 3
close(3) = 0
open("/dev/ttyS1", O_RDONLY|O_LARGEFILE <unfinished ...> {83}lsof /dev/ttyS0
{84}lsof /dev/ttyS1
{85}uname -a
Linux xxx 2.4.20-pre10aa1 #6 Fri Oct 11 13:41:20 CEST 2002 i686 unknown ---- snip ----

Quoted 4 lines

The second one was terminated with a Ctrl-C.
Nothing was connected to none of the ports.
Is there a reason that an open() on /dev/ttyS0 works and blocks on /dev/ttyS1?

Quoted 4 lines

stty -aF /dev/ttyS0
stty -aF /dev/ttyS1

I bet ttyS0 has clocal set, whereas ttyS1 doesn't.

ACK.
---- snip ----
{91}stty -aF /dev/ttyS0
speed 57600 baud; rows 0; columns 0; line = 0;
intr = ^C; quit = ^\; erase = ^?; kill = ^U; eof = ^D; eol = <undef>; eol2 = <undef>; start = ^Q; stop = ^S; susp = ^Z; rprnt = ^R; werase = ^W; lnext = ^V; flush = ^O; min = 1; time = 0;
-parenb -parodd cs8 -hupcl -cstopb cread clocal -crtscts

                                         ^^^^^^

ignbrk -brkint -ignpar -parmrk -inpck -istrip -inlcr -igncr -icrnl ixon ixoff -iuclc -ixany -imaxbel -opost -olcuc -ocrnl -onlcr -onocr -onlret -ofill -ofdel nl0 cr0 tab0 bs0 vt0 ff0
-isig -icanon -iexten -echo -echoe -echok -echonl -noflsh -xcase -tostop -echoprt -echoctl -echoke {92}stty -aF /dev/ttyS1
speed 19200 baud; rows 0; columns 0; line = 0;
intr = ^C; quit = ^\; erase = ^?; kill = ^U; eof = ^D; eol = <undef>; eol2 = <undef>; start = ^Q; stop = ^S; susp = ^Z; rprnt = ^R; werase = ^W; lnext = ^V; flush = ^O; min = 1; time = 0;
-parenb -parodd cs8 hupcl -cstopb cread -clocal crtscts

                                        ^^^^^^^

-ignbrk -brkint -ignpar -parmrk -inpck -istrip -inlcr -igncr -icrnl -ixon -ixoff -iuclc -ixany -imaxbel -opost -olcuc -ocrnl -onlcr -onocr -onlret -ofill -ofdel nl0 cr0 tab0 bs0 vt0 ff0 -isig -icanon -iexten -echo -echoe -echok -echonl -noflsh -xcase -tostop -echoprt -echoctl -echoke ---- snip ----
Sigh, perhaps reading more in Stevens' "Adv. Programming in the
Unix Environment" could help .....

Hmm, so I conclude that using something like "stty < /dev/ttyS0" is evil in general and one should always use "stty -F /dev/ttyS0" instead.

Bernd

Signature · 4 lines
Bernd Petrovitsch                              Email : [email protected]
g.a.m.s gmbh                                  Fax : +43 1 205255-900
Prinz-Eugen-Straße 8                    A-1040 Vienna/Austria/Europe
                     LUGA : http://www.luga.at
#3 lore raw
Quoted 2 lines · Bernd Petrovitsch

Hmm, so I conclude that using something like "stty < /dev/ttyS0" is evil in general and one should always use "stty -F /dev/ttyS0" instead.

Yep. stty -F uses non-blocking mode, whereas the shell doesn't.

Signature · 2 lines
Russell King ([email protected])                The developer of ARM Linux
             http://www.arm.linux.org.uk/personal/aboutme.html