kdump in upstream kexec-tools
horms at verge.net.au
Wed Apr 18 06:01:08 PDT 2018
On Tue, Apr 17, 2018 at 10:01:13AM +0100, Russell King wrote:
> On Tue, Apr 17, 2018 at 10:20:08AM +0530, Bhupesh Sharma wrote:
> > Hi,
> > I was working on improving documentation/structure of the upstream
> > kexec-tools and I was wondering what is the purpose of the 'kdump'
> > directory inside the kexec-tools.
> > This kdump utility seems to cause confusion with the 'kdump' utility
> > present inside some distributions (for e.g. '/usr/sbin/kdump' present
> > inside fedora) due to the same naming convention and so we should
> > populate/modify the kdump man page to indicate the same, so as to
> > avoid confusion.
> > Presently here are the contents of this directory:
> > # ls kdump/
> > kdump.8 kdump.c Makefile
> > - Out of these the kdump man documentation (kdump.8) is just a
> > placeholder as suggested by the man page documentation: "kdump - This
> > is just a placeholder until real man page has been written"
> > - Looking at kdump.c :
> > 1. I understand that this code is mainly used to read a crashdump from
> > memory. One can run the same using:
> > # kdump <start_addr>
> > where start_addr is basically the start address of the core dump
> > (which can also be represented via the 'elfcorehdr' environment
> > variable being passed to the crash kernel which represents the
> > physical address of the start of the ELF header)
> > 2. This tool needs READ_ONLY access to /dev/mem (so we need to set
> > CONFIG_STRICT_DEVMEM configuration option accordingly).
> > 3. The code thereafter reads (via mmap) and verifies the ELF header.
> > Subsequently it reads (via mmap) the program header.
> > 4. Then we collect all the notes and write on STDOUT all the headers
> > and notes found in the crashdump collected from memory.
> > So, as per my understanding even in absence of (more powerful) tools
> > like crash (or gdb), we can still go ahead and read the crashdump from
> > memory and display all the headers and notes present in the same on
> > standard serial out interface using this kdump utility.
> > This is probably a good to have feature for systems which have very
> > simple/minimal rootfs (and I see that a few arm32 systems seem to use
> > the same as well) or are low on memory availability.
> > Now, I wanted to confirm if the 'kdump' utility for reading crashdump
> > collected from memory is still needed (as the last commit is dated
> > back to 2016 and was done for arm32 systems). If yes, I can go ahead
> > and enhance the kdump man page to include the description given above
> > - so that it helps users understand how to run the tool.
> > Please share your opinions.
> Firstly, please use:
> for ARM systems - this has some important fixes that aren't in the
> mainline repository.
I apologise if this is due to omission on my part,
can we work towards getting them in the mainline repository?
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