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From: | Anthony Liguori |
Subject: | Re: [Qemu-devel] [PATCH] add file: migration support (r2) |
Date: | Thu, 13 Nov 2008 12:49:38 -0600 |
User-agent: | Thunderbird 2.0.0.17 (X11/20080925) |
Paul Brook wrote:
On Thursday 13 November 2008, Charles Duffy wrote:This patch adds support for migration to and from file: targets, moves common helpers between exec: and file: use cases from migration-exec.c to migration.c, and adds a qemu_fdopen() helper parallel to qemu_fopen(). Compared to the previous version submitted, it removes some cruft which was accidentally included, and documents the limitations of O_NONBLOCK on Linux with local filesystem access.I don't see any documentation.The documentation should make it clear that this is not intended as a substitute for savvm/loadvm. A "live" migration doesn't make sense if you're writing to an actual file (rather than a FIFO) as you'll end up with unecessarily large files.
Forget the large file, it's not "live" which makes it not useful compared with savevm/loadvm. Using rate limiting as a crutch to avoid this is wrong because it requires the user to know how much bandwidth QEMU can use before blocking.
To do live migration to a file, you need to tie into something like posix-aio. You could actually use a bdrv_raw and expand it like we do for a qcow file although that's sort of an abuse of the block driver API.
Regards, Anthony Liguori
Paul
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