From: "Pallipadi, Venkatesh" <venkatesh.pallipadi@intel.com>
To: <psbfan@po.harenet.ne.jp>, <linux-kernel@vger.kernel.org>
Cc: "Andrew Morton" <akpm@osdl.org>
Subject: RE: about sanitize_e820_map()
Date: Thu, 19 Jan 2006 12:47:37 -0800 [thread overview]
Message-ID: <88056F38E9E48644A0F562A38C64FB6006F49A28@scsmsx403.amr.corp.intel.com> (raw)
>Date: Thu, 12 Jan 2006 11:02:49 +0900 (JST)
>From: Toshiyuki Ishii <psbfan@po.harenet.ne.jp>
>To: linux-kernel@vger.kernel.org
>Subject: about sanitize_e820_map()
>
>
>
>Good evening.
>I am Toshiyuki Ishii at Kurashiki in Japan.
>
>I am a beginner of kernel source code,
>so sorry if I am misunderstanding.
>
>In sanitize_e820_map(),
>When sorting change_point[] by address and swapping
>two maps that represets the same memory region
>and have a different address, end address for privious change_point
>and start address for current change_point,
>"if" statement is
>
>if ((change_point[i]->addr < change_point[i-1]->addr) ||
>
> ((change_point[i]->addr == change_point[i-1]->addr) &&
> (change_point[i]->addr == change_point[i]->pbios->addr) &&
> (change_point[i-1]->addr != change_point[i-1]->pbios->addr))
>
>There are two conditions and I think the first one is sorting
>by address.
>I have a qestion in the second condition.
>
>I think second line
>
>change_point[i]->addr == change_point[i]->pbios->addr
>
>checks that current change_point represents start address.
>and third line
>
>change_point[i-1]->addr != change_point[i-1]->pbios->addr
>
>checks that previous change_point represents end address.
>If this "if" statement intends to swap maps for "the same" region
>that match these condition,
As I understand this code, this is trying to swap the start and end of
"different" regions. Start and end of same region will always be sorted
and end will appear after start (As we check for non-zero size and
setup change_point in a way that start is before end).
But, there can be end of one region coinciding with start of next
region.
In which case, this sorting puts the start before the end so that we
can properly find out overlaps later.
I think the existing code is doing the right thing.
Thanks,
Venki
next reply other threads:[~2006-01-19 20:48 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-01-19 20:47 Pallipadi, Venkatesh [this message]
-- strict thread matches above, loose matches on Subject: below --
2006-01-12 2:02 about sanitize_e820_map() Toshiyuki Ishii
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=88056F38E9E48644A0F562A38C64FB6006F49A28@scsmsx403.amr.corp.intel.com \
--to=venkatesh.pallipadi@intel.com \
--cc=akpm@osdl.org \
--cc=linux-kernel@vger.kernel.org \
--cc=psbfan@po.harenet.ne.jp \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).