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Jason A. Donenfeld 625d344978 Revert "kernel/printk: add kmsg SEEK_CUR handling" 
This reverts commit 8ece3b3eb5.

This commit broke userspace. Bash uses ESPIPE to determine whether or
not the file should be read using "unbuffered I/O", which means reading
1 byte at a time instead of 128 bytes at a time. I used to use bash to
read through kmsg in a really quite nasty way:

    while read -t 0.1 -r line 2>/dev/null || [[ $? -ne 142 ]]; do
       echo "SARU $line"
    done < /dev/kmsg

This will show all lines that can fit into the 128 byte buffer, and skip
lines that don't. That's pretty awful, but at least it worked.

With this change, bash now tries to do 1-byte reads, which means it
skips all the lines, which is worse than before.

Now, I don't really care very much about this, and I'm already look for
a workaround. But I did just spend an hour trying to figure out why my
scripts were broken. Either way, it makes no difference to me personally
whether this is reverted, but it might be something to consider. If you
declare that "trying to read /dev/kmsg with bash is terminally stupid
anyway," I might be inclined to agree with you. But do note that bash
uses lseek(fd, 0, SEEK_CUR)==>ESPIPE to determine whether or not it's
reading from a pipe.

Cc: Bruno Meneguele <bmeneg@redhat.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: David Laight <David.Laight@ACULAB.COM>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Petr Mladek <pmladek@suse.com>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-06-21 20:47:20 -07:00
..
bpf Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2020-06-13 16:27:13 -07:00
cgroup mmap locking API: convert mmap_sem comments 2020-06-09 09:39:14 -07:00
configs compiler: remove CONFIG_OPTIMIZE_INLINING entirely 2020-04-07 10:43:42 -07:00
debug maccess: rename probe_kernel_{read,write} to copy_{from,to}_kernel_nofault 2020-06-17 10:57:41 -07:00
dma dma-pool: decouple DMA_REMAP from DMA_COHERENT_POOL 2020-06-15 08:35:30 +02:00
events Merge branch 'akpm' (patches from Andrew) 2020-06-09 09:54:46 -07:00
gcov treewide: replace '---help---' in Kconfig files with 'help' 2020-06-14 01:57:21 +09:00
irq treewide: replace '---help---' in Kconfig files with 'help' 2020-06-14 01:57:21 +09:00
kcsan kcsan: Support distinguishing volatile accesses 2020-06-11 20:04:01 +02:00
livepatch livepatch: Make klp_apply_object_relocs static 2020-05-11 00:31:38 +02:00
locking The X86 entry, exception and interrupt code rework 2020-06-13 10:05:47 -07:00
power treewide: replace '---help---' in Kconfig files with 'help' 2020-06-14 01:57:21 +09:00
printk Revert "kernel/printk: add kmsg SEEK_CUR handling" 2020-06-21 20:47:20 -07:00
rcu TTY/Serial driver updates for 5.8-rc1 2020-06-07 09:52:36 -07:00
sched Rebase locking/kcsan to locking/urgent 2020-06-11 20:02:46 +02:00
time The X86 entry, exception and interrupt code rework 2020-06-13 10:05:47 -07:00
trace A few fixes and small cleanups for tracing: 2020-06-20 13:17:47 -07:00
.gitignore .gitignore: add SPDX License Identifier 2020-03-25 11:50:48 +01:00
acct.c mmap locking API: convert mmap_sem comments 2020-06-09 09:39:14 -07:00
async.c
audit_fsnotify.c fsnotify: use helpers to access data by data_type 2020-03-23 18:19:06 +01:00
audit_tree.c
audit_watch.c \n 2020-04-06 08:58:42 -07:00
audit.c audit/stable-5.8 PR 20200601 2020-06-02 17:13:37 -07:00
audit.h audit: fix a net reference leak in audit_list_rules_send() 2020-04-22 15:23:10 -04:00
auditfilter.c audit: fix a net reference leak in audit_list_rules_send() 2020-04-22 15:23:10 -04:00
auditsc.c audit: add subj creds to NETFILTER_CFG record to 2020-05-20 18:09:19 -04:00
backtracetest.c
bounds.c
capability.c
compat.c uaccess: Selectively open read or write user access 2020-05-01 12:35:21 +10:00
configs.c proc: convert everything to "struct proc_ops" 2020-02-04 03:05:26 +00:00
context_tracking.c context_tracking: Ensure that the critical path cannot be instrumented 2020-06-11 15:14:36 +02:00
cpu_pm.c kernel/cpu_pm: Fix uninitted local in cpu_pm 2020-05-15 11:44:34 -07:00
cpu.c The changes in this cycle are: 2020-06-03 13:06:42 -07:00
crash_core.c
crash_dump.c crash_dump: Remove no longer used saved_max_pfn 2020-04-15 11:21:54 +02:00
cred.c exec: Teach prepare_exec_creds how exec treats uids & gids 2020-05-20 14:44:21 -05:00
delayacct.c
dma.c
elfcore.c
exec_domain.c
exit.c mmap locking API: convert mmap_sem comments 2020-06-09 09:39:14 -07:00
extable.c kernel/extable.c: use address-of operator on section symbols 2020-04-07 10:43:42 -07:00
fail_function.c
fork.c mmap locking API: convert nested write lock sites 2020-06-09 09:39:14 -07:00
freezer.c
futex.c mmap locking API: use coccinelle to convert mmap_sem rwsem call sites 2020-06-09 09:39:14 -07:00
gen_kheaders.sh kbuild: add variables for compression tools 2020-06-06 23:42:01 +09:00
groups.c mm: remove the pgprot argument to __vmalloc 2020-06-02 10:59:11 -07:00
hung_task.c kernel/hung_task.c: introduce sysctl to print all traces when a hung task is detected 2020-06-08 11:05:56 -07:00
iomem.c
irq_work.c irq_work, smp: Allow irq_work on call_single_queue 2020-05-28 10:54:15 +02:00
jump_label.c
kallsyms.c kallsyms: unexport kallsyms_lookup_name() and kallsyms_on_each_symbol() 2020-04-07 10:43:44 -07:00
kcmp.c kernel/kcmp.c: Use new infrastructure to fix deadlocks in execve 2020-03-25 10:04:01 -05:00
Kconfig.freezer
Kconfig.hz
Kconfig.locks
Kconfig.preempt
kcov.c kcov: check kcov_softirq in kcov_remote_stop() 2020-06-10 19:14:17 -07:00
kexec_core.c
kexec_elf.c
kexec_file.c kexec_file: don't place kexec images on IORESOURCE_MEM_DRIVER_MANAGED 2020-06-04 19:06:23 -07:00
kexec_internal.h
kexec.c
kheaders.c
kmod.c kmod: make request_module() return an error when autoloading is disabled 2020-04-10 15:36:22 -07:00
kprobes.c kretprobe: Prevent triggering kretprobe from within kprobe_flush_task 2020-06-16 21:21:01 -04:00
ksysfs.c
kthread.c maccess: rename probe_kernel_{read,write} to copy_{from,to}_kernel_nofault 2020-06-17 10:57:41 -07:00
latencytop.c sysctl: pass kernel pointers to ->proc_handler 2020-04-27 02:07:40 -04:00
Makefile Notifications over pipes + Keyring notifications 2020-06-13 09:56:21 -07:00
module_signature.c
module_signing.c
module-internal.h
module.c module: move the set_fs hack for flush_icache_range to m68k 2020-06-08 11:05:58 -07:00
notifier.c mm: remove vmalloc_sync_(un)mappings() 2020-06-02 10:59:12 -07:00
nsproxy.c nsproxy: attach to namespaces via pidfds 2020-05-13 11:41:22 +02:00
padata.c padata: add basic support for multithreaded jobs 2020-06-03 20:09:45 -07:00
panic.c bug: Annotate WARN/BUG/stackfail as noinstr safe 2020-06-11 15:14:36 +02:00
params.c
pid_namespace.c Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next 2020-06-03 16:27:18 -07:00
pid.c remove the no longer needed pid_alive() check in __task_pid_nr_ns() 2020-04-30 06:40:14 -05:00
profile.c proc: convert everything to "struct proc_ops" 2020-02-04 03:05:26 +00:00
ptrace.c ptrace: reintroduce usage of subjective credentials in ptrace_has_cap() 2020-01-18 13:51:39 +01:00
range.c
reboot.c printk: Collapse shutdown types into a single dump reason 2020-05-30 10:34:03 -07:00
relay.c mmap locking API: convert mmap_sem comments 2020-06-09 09:39:14 -07:00
resource.c /dev/mem: Revoke mappings when a driver claims the region 2020-05-27 11:10:05 +02:00
rseq.c
scs.c scs: Report SCS usage in bytes rather than number of entries 2020-06-04 16:14:56 +01:00
seccomp.c sysctl: pass kernel pointers to ->proc_handler 2020-04-27 02:07:40 -04:00
signal.c Merge branch 'work.set_fs-exec' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2020-06-01 16:21:46 -07:00
smp.c The changes in this cycle are: 2020-06-03 13:06:42 -07:00
smpboot.c
smpboot.h
softirq.c x86/entry: Clarify irq_{enter,exit}_rcu() 2020-06-11 15:15:24 +02:00
stackleak.c
stacktrace.c
stop_machine.c stop_machine: Make stop_cpus() static 2020-01-17 10:19:21 +01:00
sys_ni.c
sys.c Add additional LSM hooks for SafeSetID 2020-06-14 11:39:31 -07:00
sysctl_binary.c
sysctl-test.c kunit: allow kunit tests to be loaded as a module 2020-01-09 16:42:29 -07:00
sysctl.c kernel/sysctl.c: ignore out-of-range taint bits introduced via kernel.tainted 2020-06-08 11:05:56 -07:00
task_work.c task_work_run: don't take ->pi_lock unconditionally 2020-03-02 14:06:33 -07:00
taskstats.c
test_kprobes.c
torture.c CPU (hotplug) updates: 2020-03-30 18:06:39 -07:00
tracepoint.c
tsacct.c
ucount.c ucount: Make sure ucounts in /proc/sys/user don't regress again 2020-04-07 21:51:27 +02:00
uid16.c
uid16.h
umh.c Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2020-05-15 13:48:59 -07:00
up.c smp/up: Make smp_call_function_single() match SMP semantics 2020-02-07 15:34:12 +01:00
user_namespace.c nsproxy: add struct nsset 2020-05-09 13:57:12 +02:00
user-return-notifier.c
user.c user.c: make uidhash_table static 2020-06-04 19:06:24 -07:00
utsname_sysctl.c sysctl: pass kernel pointers to ->proc_handler 2020-04-27 02:07:40 -04:00
utsname.c nsproxy: add struct nsset 2020-05-09 13:57:12 +02:00
watch_queue.c Notifications over pipes + Keyring notifications 2020-06-13 09:56:21 -07:00
watchdog_hld.c
watchdog.c kernel/watchdog.c: convert {soft/hard}lockup boot parameters to sysctl aliases 2020-06-08 11:05:56 -07:00
workqueue_internal.h
workqueue.c maccess: rename probe_kernel_{read,write} to copy_{from,to}_kernel_nofault 2020-06-17 10:57:41 -07:00