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bootm: Fix Linux silent console on newer kernels

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Linux determines its console based on several sources:

1. the console command line parameter
2. device tree (e.g. /chosen/stdout-path)
3. various other board- and arch-specific sources

If the console parameter specifies a real console (e.g. ttyS0) then that is
used as /dev/console. However, if it does not specify a real console (e.g.
ttyDoesntExist) then *nothing* will be used as /dev/console.
Reading/writing it will return ENODEV. Additionally, no other source will
be used as a console source.

Linux commit ab4af56ae250 ("printk/console: Allow to disable console output
by using console="" or console=null") recently changed the semantics of the
parameter. Previously, specifying console="" would be treated like
specifying some other bad console. This commit changed things so that it
added /dev/ttynull as a console (if available).  However, it also allows
for other console sources. If the device tree specifies a console (such as
if U-Boot and Linux share a device tree), then it will be used in addition
to /dev/ttynull. This can result in a non-silent console.

To avoid this, explicitly set ttynull as the console. This will disable
other console sources. If CONFIG_NULL_TTY is disabled, then this will have
the same behavior as in the past (no output, and writing /dev/console
returns ENODEV).

[1] and [2] have additional background on this kernel change.

[1] https://lore.kernel.org/all/20201006025935.GA597@jagdpanzerIV.localdomain/
[2] https://lore.kernel.org/all/20201111135450.11214-1-pmladek@suse.com/

Signed-off-by: Sean Anderson <sean.anderson@seco.com>
This commit is contained in:
Sean Anderson 2022-05-19 18:26:05 -04:00 • committed by Tom Rini
parent f2ebaaa9f3
commit ba9aa40bb3
2 changed files with 19 additions and 17 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

16
boot/bootm.c
View file

@ -498,7 +498,8 @@ ulong bootm_disable_interrupts(void)
}
#define CONSOLE_ARG "console="
#define CONSOLE_ARG_SIZE sizeof(CONSOLE_ARG)
#define NULL_CONSOLE (CONSOLE_ARG "ttynull")
#define CONSOLE_ARG_SIZE sizeof(NULL_CONSOLE)
/**
* fixup_silent_linux() - Handle silencing the linux boot if required
@ -550,21 +551,22 @@ static int fixup_silent_linux(char *buf, int maxlen)
char *end = strchr(start, ' ');
int start_bytes;
start_bytes = start - cmdline + CONSOLE_ARG_SIZE - 1;
start_bytes = start - cmdline;
strncpy(buf, cmdline, start_bytes);
strncpy(buf + start_bytes, NULL_CONSOLE, CONSOLE_ARG_SIZE);
if (end)
strcpy(buf + start_bytes, end);
strcpy(buf + start_bytes + CONSOLE_ARG_SIZE - 1, end);
else
buf[start_bytes] = '\0';
buf[start_bytes + CONSOLE_ARG_SIZE] = '\0';
} else {
sprintf(buf, "%s %s", cmdline, CONSOLE_ARG);
sprintf(buf, "%s %s", cmdline, NULL_CONSOLE);
}
if (buf + strlen(buf) >= cmdline)
return -ENOSPC;
} else {
if (maxlen < sizeof(CONSOLE_ARG))
if (maxlen < CONSOLE_ARG_SIZE)
return -ENOSPC;
strcpy(buf, CONSOLE_ARG);
strcpy(buf, NULL_CONSOLE);
}
debug("after silent fix-up: %s\n", buf);

20
test/bootm.c
View file

@ -83,12 +83,12 @@ static int bootm_test_silent(struct unit_test_state *uts)
ut_assertok(env_set("silent_linux", "yes"));
ut_assertok(bootm_process_cmdline(buf, BUF_SIZE, BOOTM_CL_SILENT));
ut_asserteq_str("console=", buf);
ut_asserteq_str("console=ttynull", buf);
/* Empty buffer should still add the string */
*buf = '\0';
ut_assertok(bootm_process_cmdline(buf, BUF_SIZE, BOOTM_CL_SILENT));
ut_asserteq_str("console=", buf);
ut_asserteq_str("console=ttynull", buf);
/* Check nothing happens when do_silent is false */
*buf = '\0';
@ -97,21 +97,21 @@ static int bootm_test_silent(struct unit_test_state *uts)
/* Not enough space */
*buf = '\0';
ut_asserteq(-ENOSPC, bootm_process_cmdline(buf, 8, BOOTM_CL_SILENT));
ut_asserteq(-ENOSPC, bootm_process_cmdline(buf, 15, BOOTM_CL_SILENT));
/* Just enough space */
*buf = '\0';
ut_assertok(bootm_process_cmdline(buf, 9, BOOTM_CL_SILENT));
ut_assertok(bootm_process_cmdline(buf, 16, BOOTM_CL_SILENT));
/* add at end */
strcpy(buf, "something");
ut_assertok(bootm_process_cmdline(buf, BUF_SIZE, BOOTM_CL_SILENT));
ut_asserteq_str("something console=", buf);
ut_asserteq_str("something console=ttynull", buf);
/* change at start */
strcpy(buf, CONSOLE_STR " something");
ut_assertok(bootm_process_cmdline(buf, BUF_SIZE, BOOTM_CL_SILENT));
ut_asserteq_str("console= something", buf);
ut_asserteq_str("console=ttynull something", buf);
return 0;
}
@ -210,12 +210,12 @@ static int bootm_test_subst_var(struct unit_test_state *uts)
{
env_set("bootargs", NULL);
ut_assertok(bootm_process_cmdline_env(BOOTM_CL_SILENT));
ut_asserteq_str("console=", env_get("bootargs"));
ut_asserteq_str("console=ttynull", env_get("bootargs"));
ut_assertok(env_set("var", "abc"));
ut_assertok(env_set("bootargs", "some${var}thing"));
ut_assertok(bootm_process_cmdline_env(BOOTM_CL_SILENT));
ut_asserteq_str("some${var}thing console=", env_get("bootargs"));
ut_asserteq_str("some${var}thing console=ttynull", env_get("bootargs"));
return 0;
}
@ -227,12 +227,12 @@ static int bootm_test_subst_both(struct unit_test_state *uts)
ut_assertok(env_set("silent_linux", "yes"));
env_set("bootargs", NULL);
ut_assertok(bootm_process_cmdline_env(BOOTM_CL_ALL));
ut_asserteq_str("console=", env_get("bootargs"));
ut_asserteq_str("console=ttynull", env_get("bootargs"));
ut_assertok(env_set("bootargs", "some${var}thing " CONSOLE_STR));
ut_assertok(env_set("var", "1234567890"));
ut_assertok(bootm_process_cmdline_env(BOOTM_CL_ALL));
ut_asserteq_str("some1234567890thing console=", env_get("bootargs"));
ut_asserteq_str("some1234567890thing console=ttynull", env_get("bootargs"));
return 0;
}