Re: [Crash-utility] [PATCH 0/7] Upgrade the remote access to a xen domain.

On 11/19/13 11:08, Dave Anderson wrote: > > ----- Original Message ----- >> From: Don Slutz <dslutz(a)verizon.com&gt; >> >> Currently crash 4.0 and later using the code: >> >> http://lists.xen.org/archives/html/xen-devel/2013-11/msg02569.html >> >> There is some very limited documention on crashes remote ptotocol in: >> >> http://lists.xen.org/archives/html/xen-devel/2013-11/msg02352.html >> >> and some fixes in the attachment >> 0001-xen-crashd-Connect-crash-with-domain.patch >> from the 1st link above. >> >> How ever there are issues with the current code: >> >> 1) The remote protocol has a minor issue (which I have not been able to >> happen) based on the fact TCP/IP is stream based protocol. This means >> a RECV or a SEND may not do the fully requested size of data. In fact >> the current code assumes that the amount of data that a SEND is called >> with will all be read with a single RECV. >> >> 2) The most common mismatch between crash and older kernels is >> phys_base. In the remote case, see if the remote server supports >> vitrual memory access, and if so, see if phys_base can be retreived. >> >> 3) crash assumes that the remote system is active and can not return >> currect IP and SP to do a better back trace. >> >> 4) enable a non-active mode of remote access. >> >> This patch set attempts to fix these: >> >> The fix for #1 I have called NIL mode (patch 1). >> The fix for #2 uses get_remote_phys_base (patch 3). >> The fix for #3 uses get_remote_regs (patch 5). >> The fix for #4 uses special file /dev/xenmem (patch 7). >> It also REMOTE_NIL() to indicate "remote paused system". >> >> Don Slutz (7): >> Add NIL mode to remote. >> remote_proc_version: NULL terminate passed buffer on error. >> Add get_remote_phys_base. >> Add remote_vtop. >> bt: get remote live registers if possible. >> Add get_remote_cr3 >> Add support for non-live remote. >> >> defs.h | 8 +- >> kernel.c | 25 +++- >> memory.c | 25 +++- >> remote.c | 462 >> +++++++++++++++++++++++++++++++++++++++++++++++++++++---------- >> x86_64.c | 24 ++++ >> 5 files changed, 465 insertions(+), 79 deletions(-) >> >> -- >> 1.8.4 > > Hi Don, > > A few comments... > > I don't really understand what entity the code is communicating with, > so for the most part, I'm primarily interested in making sure that your > patches in no way can affect the normal usage of the crash utility. > > That being said, is the term "NIL mode" some kind of Xen-ism? Nope, it is term I came up with to describe the protocol change. > It wasn't > until I saw the display_sys_stats() function that I even understood that > REMOTE_NIL mean "(remote paused system)". Anyway, if you made it something > like "REMOTE_PAUSED" or something like that, the code might make some sense > to the untrained eye. Will do. Looking back at it, I ended up overloading the term. :( > > And it's not entirely clear to me what REMOTE_ACTIVE() means now? It used > to imply communicating with a remote crash daeamon that accessed the live > system that the daemon was running on. Has that meaning been changed to > mean > that crash is communicating with a daemon that's accessing a "live" Xen > guest > kernel? The meaning is not as clear. Since the existing versions of crash already have REMOTE_ACTIVE() and I wanted the Xen utility to be usable to them, in both cases the "live" Xen guest kernel is being accessed while it is paused. I added REMOTE_PAUSED() to have a few changes to crash to correctly understand that the guest is paused. As part of this I add the fake file "/dev/xenmem". > > I'm confused about these two changes, where you re-patch your own patch: > > - else > + else if (REMOTE_ACTIVE() && ((bt->task == tt->this_task) || > is_task_active(bt->task))) { > + if (get_remote_regs(bt, &eip, &esp)) > + machdep->get_stack_frame(bt, &eip, &esp); > + } else > > followed by: > > - else if (REMOTE_ACTIVE() && ((bt->task == tt->this_task) || > is_task_active(bt->task))) { > + else if (REMOTE_NIL() && ((bt->task == tt->this_task) || > is_task_active(bt->task))) { > if (get_remote_regs(bt, &eip, &esp)) > machdep->get_stack_frame(bt, &eip, &esp); > } else Clearly I need to adjust the patch order. > If I'm not mistaken, it would seem to be impossible for "(bt->task == > tt->this_task)" > to ever be true in the REMOTE_NIL() case? As I recall tt->this_task used > to be the > PID of the remote daemon itself, which would be accessing the memory of its > own kernel. > So how could the pid of the remote daemon ever be the target of a back > trace of a > paused guest? And so I don't understand why you first made an if clause > for > REMOTE_ACTIVE() to begin with -- whatever that means now -- and then > changed it to > REMOTE_NIL()? This came about from some old changes from 2012 to a crash version 4.0 for other work. I had not thought of /dev/xenmem at the time, and just copied the condition from above. I see no reason not to drop "bt->task == tt->this_task". Will check that the right actions are still done. > In any case, since the ultimate change is only interested in REMOTE_NIL(), > can you make it all less of an eyesore by encapulating its if case > something like: > > else if (SADUMP_DUMPFILE()) > get_sadump_regs(bt, &eip, &esp); > + else if (REMOTE_NIL()) { > + if (!((bt->task == tt->this_task) || > is_task_active(bt->task)) || > + !get_remote_regs(bt, &eip, &esp)) > + machdep->get_stack_frame(bt, &eip, &esp); > } else > machdep->get_stack_frame(bt, &eip, &esp); > > Note above, for consistency's sake with the rest of the crash utility, > can you make get_remote_regs() return non-zero when it successfully gets > the registers, and zero if it fails? Sure. > And lastly, can you fix these? > > $ make warn > ... > remote.c: In function ‘validate_phys_base’: > remote.c:2302:25: warning: format ‘%llx’ expects argument of type > ‘long long unsigned int’, but argument 3 has type ‘physaddr_t’ > [-Wformat] > remote.c:2302:25: warning: format ‘%llx’ expects argument of type > ‘long long unsigned int’, but argument 4 has type ‘physaddr_t’ > [-Wformat] > remote.c:2302:25: warning: format ‘%llx’ expects argument of type > ‘long long unsigned int’, but argument 5 has type ‘physaddr_t’ > [-Wformat] > remote.c:2302:25: warning: format ‘%llx’ expects argument of type > ‘long long unsigned int’, but argument 6 has type ‘physaddr_t’ > [-Wformat] > remote.c: In function ‘remote_vtop’: > remote.c:2361:2: warning: format ‘%llx’ expects argument of type > ‘long long unsigned int’, but argument 4 has type ‘physaddr_t’ > [-Wformat] > remote.c:2367:4: warning: format ‘%llx’ expects argument of type > ‘long long unsigned int’, but argument 4 has type ‘physaddr_t’ > [-Wformat] > remote.c:2352:18: warning: variable ‘p3’ set but not used > [-Wunused-but-set-variable] > remote.c:2352:13: warning: variable ‘p2’ set but not used > [-Wunused-but-set-variable] > remote.c:2352:8: warning: variable ‘p1’ set but not used > [-Wunused-but-set-variable] > remote.c: In function ‘get_remote_regs’: > remote.c:2392:33: warning: unused variable ‘p6’ [-Wunused-variable] > remote.c:2392:28: warning: variable ‘p5’ set but not used > [-Wunused-but-set-variable] > remote.c:2392:18: warning: variable ‘p3’ set but not used > [-Wunused-but-set-variable] > remote.c:2392:8: warning: variable ‘p1’ set but not used > [-Wunused-but-set-variable] > remote.c: In function ‘get_remote_cr3’: > remote.c:2449:13: warning: variable ‘p2’ set but not used > [-Wunused-but-set-variable] > remote.c:2449:8: warning: variable ‘p1’ set but not used > [-Wunused-but-set-variable] > ... Yes. > And I'm not interested in appending these to the 4 files that you changed: > > +/* > + * Specify Emacs local variables so the formating > + * of the code stays the same. > + * > + * Local variables: > + * mode: C > + * c-set-style: "BSD" > + * c-basic-offset: 8 > + * indent-tabs-mode: t > + * End: > + */ > > Thanks, > Dave Ok, that is 2 votes to drop this, so I will. -Don Slutz