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SubjectRe: [RFC PATCH v4 01/10] fadump: Add documentation for firmware-assisted dump.
On 2011-11-10 17:46:30 Thu, Cong Wang wrote:
> 于 2011年11月07日 17:55, Mahesh J Salgaonkar 写道:
> >From: Mahesh Salgaonkar<mahesh@linux.vnet.ibm.com>
> >
> >Documentation for firmware-assisted dump. This document is based on the
> >original documentation written for phyp assisted dump by Linas Vepstas
> >and Manish Ahuja, with few changes to reflect the current implementation.
> >
> >Change in v3:
> >- Modified the documentation to reflect introdunction of fadump_registered
> > sysfs file and few minor changes.
> >
> >Change in v2:
> >- Modified the documentation to reflect the change of fadump_region
> > file under debugfs filesystem.
> >
> >Signed-off-by: Mahesh Salgaonkar<mahesh@linux.vnet.ibm.com>
>
>
> Please Cc Randy Dunlap <rdunlap@xenotime.net> for kernel documentation
> patch.
>
> I have some inline comments below.
>

Thanks for your review. I will incorporate all your comments.

<...>
> >+with minor modifications. The kdump script requires following
> >+modifications:
> >+-- During service kdump start if /proc/vmcore entry is not present,
> >+ look for the existence of /sys/kernel/fadump_enabled and read
> >+ value exported by it. If value is set to '0' then fallback to
> >+ existing kexec based kdump. If value is set to '1' then check the
> >+ value exported by /sys/kernel/fadump_registered. If value it set
> >+ to '1' then print success otherwise register for fadump by
> >+ echo'ing 1> /sys/kernel/fadump_registered file.
> >+
> >+-- During service kdump start if /proc/vmcore entry is present,
> >+ execute the existing routine to save the dump. Once the dump
> >+ is saved, echo 1> /sys/kernel/fadump_release_mem (if the
> >+ file exists) to release the reserved memory for general use
> >+ and continue without rebooting. At this point the memory
> >+ reservation map will look like as shown in Fig. 1. If the file
> >+ /sys/kernel/fadump_release_mem is not present then follow
> >+ the existing routine to reboot into new kernel.
> >+
> >+-- During service kdump stop echo 0> /sys/kernel/fadump_registered
> >+ to un-register the fadump.
> >+
>
> I don't think you need to document kdump script changes in a kernel
> doc.
>

Agree. I will remove it.

> >+
> >+TODO:
> >+-----
> >+ o Need to come up with the better approach to find out more
> >+ accurate boot memory size that is required for a kernel to
> >+ boot successfully when booted with restricted memory.
> >+ o The fadump implementation introduces a fadump crash info structure
> >+ in the scratch area before the ELF core header. The idea of introducing
> >+ this structure is to pass some important crash info data to the second
> >+ kernel which will help second kernel to populate ELF core header with
> >+ correct data before it gets exported through /proc/vmcore. The current
> >+ design implementation does not address a possibility of introducing
> >+ additional fields (in future) to this structure without affecting
> >+ compatibility. Need to come up with the better approach to address this.
> >+ The possible approaches are:
> >+ 1. Introduce version field for version tracking, bump up the version
> >+ whenever a new field is added to the structure in future. The version
> >+ field can be used to find out what fields are valid for the current
> >+ version of the structure.
> >+ 2. Reserve the area of predefined size (say PAGE_SIZE) for this
> >+ structure and have unused area as reserved (initialized to zero)
> >+ for future field additions.
> >+ The advantage of approach 1 over 2 is we don't need to reserve extra space.
> >+---
>
> Why do we keep TODO in this doc?
>

I see most of the kernel doc do contain TODO, hence I added it here.

Thanks,
-Mahesh.

--
Mahesh J Salgaonkar

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