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Using z/VM the 3270 terminal emulator also emulates an IBM 3215 console which outputs line by line. When the screen is full, the console enters the MORE... state and waits for the operator to confirm the data on the screen by pressing a clear key. If this does not happen in the default time frame (currently 50 seconds) the console enters the HOLDING state. It then waits another time frame (currently 10 seconds) before the output continues on the next screen. When the operator presses the clear key during these wait times, the output continues immediately. This may lead to a very long boot time when the console has to print many messages, also the system may hang because of the console's limited buffer space and the system waits for the console output to drain and finally to finish. This problem can only occur when a terminal emulator is actually connected to the 3215 console driver. If not z/VM simply drops console output. Remedy this rare situation and add a kernel boot command line parameter con3215_drop. It can be set to 0 (do not drop) or 1 (do drop) which is the default. This instructs the kernel drop console data when the console buffer is full. This speeds up the boot time considerable and also does not hang the system anymore. Add a sysfs attribute file for console IBM 3215 named con_drop. This allows for changing the behavior after the boot, for example when during interactive debugging a panic/crash is expected. Here is a test of the new behavior using the following test program: #/bin/bash declare -i cnt=4 mode=$(cat /sys/bus/ccw/drivers/3215/con_drop) [ $mode = yes ] && cnt=25 echo "cons_drop $(cat /sys/bus/ccw/drivers/3215/con_drop)" echo "vmcp term more 5 2" vmcp term more 5 2 echo "Run $cnt iterations of "'echo t > /proc/sysrq-trigger' for i in $(seq $cnt) do echo "$i. command 'echo t > /proc/sysrq-trigger' at $(date +%F,%T)" echo t > /proc/sysrq-trigger sleep 1 done echo "droptest done" > /dev/kmsg # Output with sysfs attribute con_drop set to 1: # ./droptest.sh cons_drop yes vmcp term more 5 2 Run 25 iterations of echo t > /proc/sysrq-trigger 1. command 'echo t > /proc/sysrq-trigger' at 2022-09-02,10:15:09 2. command 'echo t > /proc/sysrq-trigger' at 2022-09-02,10:15:10 3. command 'echo t > /proc/sysrq-trigger' at 2022-09-02,10:15:11 4. command 'echo t > /proc/sysrq-trigger' at 2022-09-02,10:15:12 5. command 'echo t > /proc/sysrq-trigger' at 2022-09-02,10:15:13 6. command 'echo t > /proc/sysrq-trigger' at 2022-09-02,10:15:14 7. command 'echo t > /proc/sysrq-trigger' at 2022-09-02,10:15:15 8. command 'echo t > /proc/sysrq-trigger' at 2022-09-02,10:15:16 9. command 'echo t > /proc/sysrq-trigger' at 2022-09-02,10:15:17 10. command 'echo t > /proc/sysrq-trigger' at 2022-09-02,10:15:18 11. command 'echo t > /proc/sysrq-trigger' at 2022-09-02,10:15:19 12. command 'echo t > /proc/sysrq-trigger' at 2022-09-02,10:15:20 13. command 'echo t > /proc/sysrq-trigger' at 2022-09-02,10:15:21 14. command 'echo t > /proc/sysrq-trigger' at 2022-09-02,10:15:22 15. command 'echo t > /proc/sysrq-trigger' at 2022-09-02,10:15:23 16. command 'echo t > /proc/sysrq-trigger' at 2022-09-02,10:15:24 17. command 'echo t > /proc/sysrq-trigger' at 2022-09-02,10:15:25 18. command 'echo t > /proc/sysrq-trigger' at 2022-09-02,10:15:26 19. command 'echo t > /proc/sysrq-trigger' at 2022-09-02,10:15:27 20. command 'echo t > /proc/sysrq-trigger' at 2022-09-02,10:15:28 21. command 'echo t > /proc/sysrq-trigger' at 2022-09-02,10:15:29 22. command 'echo t > /proc/sysrq-trigger' at 2022-09-02,10:15:30 23. command 'echo t > /proc/sysrq-trigger' at 2022-09-02,10:15:31 24. command 'echo t > /proc/sysrq-trigger' at 2022-09-02,10:15:32 25. command 'echo t > /proc/sysrq-trigger' at 2022-09-02,10:15:33 # There are no hangs anymore. Output with sysfs attribute con_drop set to 0 and identical setting for z/VM console 'term more 5 2'. Sometimes hitting the clear key at the x3270 console to progress output. # ./droptest.sh cons_drop no vmcp term more 5 2 Run 4 iterations of echo t > /proc/sysrq-trigger 1. command 'echo t > /proc/sysrq-trigger' at 2022-09-02,10:20:58 2. command 'echo t > /proc/sysrq-trigger' at 2022-09-02,10:24:32 3. command 'echo t > /proc/sysrq-trigger' at 2022-09-02,10:28:04 4. command 'echo t > /proc/sysrq-trigger' at 2022-09-02,10:31:37 # Details: Enable function raw3215_write() to handle tab expansion and newlines and feed it with input not larger than the console buffer of 65536 bytes. Function raw3125_putchar() just forwards its character for output to raw3215_write(). This moves tab to blank conversion to one function raw3215_write() which also does call raw3215_make_room() to wait for enough free buffer space. Function handle_write() loops over all its input and segments input into chunks of console buffer size (should the input be larger). Rework tab expansion handling logic to avoid code duplication. Signed-off-by: Thomas Richter <tmricht@linux.ibm.com> Acked-by: Peter Oberparleiter <oberpar@linux.ibm.com> Acked-by: Heiko Carstens <hca@linux.ibm.com> Signed-off-by: Vasily Gorbik <gor@linux.ibm.com> |
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| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| io_uring | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| rust | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| .rustfmt.toml | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.