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From: | Michael Tokarev |
Subject: | Re: [Qemu-devel] [PATCH] Add readonly flag to -drive command |
Date: | Mon, 12 Oct 2009 20:15:43 +0400 |
User-agent: | Mozilla-Thunderbird 2.0.0.22 (X11/20090706) |
Anthony Liguori wrote:
Jamie Lokier wrote:Kevin Wolf wrote:Am 12.10.2009 14:47, schrieb Naphtali Sprei:In order to safely share an image between guests (as read only drive), add a 'readonly' flagto the -drive command (qemu command line and monitor).Heh. I've been sharing images between guests for ages - using "chmod -r" :-)Were it not for backwards compatibility, I would remove that and have it error out.I've had multiple people end up with strangely broken guests because they didn't realize the image was read only.
And I had this issue too. But for me it's still not clear. Some disk drives out there can be switched to read-only mode at runtime by using appropriate command. Certain (USB and especially SD) flash drives can be read-only too (usually a tiny swith does that). Even old good floppy drives had a "write protect" switch. How the system determines if such devices are read-only? For a HDD or a flash drive, I *guess* the drive return appropriate error message, no? But qemu - apparently - just ignores writes in this case, which results in stalled guest which expects some answer to the write command.. I guess, because it was always the stalls. /mjt
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