[Crash-utility] [RFC/PATCH] s390x: Add live dump detection

Hi Dave, On s390 we will have a dump method that creates live dumps, similar to the snap.so crash plugin. Because Linux is not stopped while the dump is created, the resulting dump is not consistent. Therefore it is important that the crash tool informs the user about this issue. The dump tool writes a magic number (ASCII "LIVEDUMP") into the first 8 bytes of the dump memory. With this patch this is checked in POST_INIT by the s390x backend crash code. If the magic is found, the LIVE_SYSTEM flag is set. This ensures that commands that do not work with /dev/mem also will fail with s390x live dumps. Example: crash> bt -a bt: -a option not supported on a live system In addition to that with this patch crash prints a "[LIVE DUMP]" info tag for live dump files at startup (similar to [PARTIAL DUMP]): $ crash livedump vmlinux KERNEL: /boot/vmlinux DUMPFILE: dump.s390 [LIVE DUMP] Michael --- kernel.c | 8 ++++++-- s390x.c | 12 ++++++++++++ 2 files changed, 18 insertions(+), 2 deletions(-) --- a/kernel.c +++ b/kernel.c @@ -975,7 +975,9 @@ non_matching_kernel(void) else fprintf(fp, " DUMPFILE: "); if (ACTIVE()) { - if (REMOTE_ACTIVE()) + if (pc->dumpfile) + fprintf(fp, "%s [LIVE DUMP]\n", pc->dumpfile); + else if (REMOTE_ACTIVE()) fprintf(fp, "%s@%s (remote live system)\n", pc->server_memsrc, pc->server); else @@ -4080,7 +4082,9 @@ display_sys_stats(void) else fprintf(fp, " DUMPFILE: "); if (ACTIVE()) { - if (REMOTE_ACTIVE()) + if (pc->dumpfile) + fprintf(fp, "%s [LIVE DUMP]\n", pc->dumpfile); + else if (REMOTE_ACTIVE()) fprintf(fp, "%s@%s (remote live system)\n", pc->server_memsrc, pc->server); else --- a/s390x.c +++ b/s390x.c @@ -328,6 +328,17 @@ static void s390x_process_elf_notes(void } } +static void s390x_check_live(void) +{ + unsigned long long live_magic; + + readmem(0, KVADDR, &live_magic, sizeof(live_magic), "live_magic", + RETURN_ON_ERROR | QUIET); + + if (live_magic == 0x4c49564544554d50ULL) + pc->flags |= LIVE_SYSTEM; +} + /* * Do all necessary machine-specific setup here. This is called several * times during initialization. @@ -402,6 +413,7 @@ s390x_init(int when) break; case POST_INIT: + s390x_check_live(); break; } }