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Re: [Qemu-devel] [PATCH] Add readonly flag to -drive command
From: |
Kevin Wolf |
Subject: |
Re: [Qemu-devel] [PATCH] Add readonly flag to -drive command |
Date: |
Mon, 12 Oct 2009 15:24:06 +0200 |
User-agent: |
Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.1) Gecko/20090814 Fedora/3.0-2.6.b3.fc11 Thunderbird/3.0b3 |
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' flag
> to the -drive command (qemu command line and monitor).
>
> Still missing passing the read only attribute to the guest, where possible. I
> don't know which device types supports
> read only, and don't know how to pass this information to guests.
>
> Also not sure what to do when qemu cannot open the file as writeable.
> Currently it opens it as read only.
> We might change it to give a warning or even an error.
>
> From 6e297da79a4c015555e3927e6d28744933a31ebe Mon Sep 17 00:00:00 2001
> From: Naphtali Sprei <address@hidden>
> Date: Mon, 12 Oct 2009 14:25:25 +0200
> Subject: [PATCH] Added readonly flag to -drive command.
> This enables sharing same image between guests, with readonly access.
> Implementaion mark the drive as read_only and changes the flags when
> actually opening the file.
Is this enough? Basically none of the block drivers know that their
image could be read-only, so we'll likely trigger some unexpected error
cases there. For a simple write I guess we'll be okay (not sure if we'll
return the right error code, though), but I have no idea what, say,
savevm would do with a read-only image.
What cases have you tested?
> TODO:
> 1. Pass the readonly attribute to the guest (write-protected drive ??)
I agree. To be useful the read-only attribute should be exposed to the
guest. I think most devices support some sort of write protection.
> 2. Re-visit the scheme where qemu open a file (silently) in read only mode
> when it can't open for write.
> Now that user can specify read only (and didn't), might give a warning
> when not writeable, or even
> give an error.
>
> Signed-off-by: Naphtali Sprei <address@hidden>
> ---
> block.c | 14 ++++++++++++--
> block.h | 1 +
> qemu-config.c | 3 +++
> vl.c | 6 ++++++
> 4 files changed, 22 insertions(+), 2 deletions(-)
>
> diff --git a/block.c b/block.c
> index 33f3d65..01fd289 100644
> --- a/block.c
> +++ b/block.c
> @@ -335,7 +335,8 @@ int bdrv_open2(BlockDriverState *bs, const char
> *filename, int flags,
> char tmp_filename[PATH_MAX];
> char backing_filename[PATH_MAX];
>
> - bs->read_only = 0;
> + /* don't mess with it, should have been zeros, anyway */
> + /* bs->read_only = 0; */
Why leave that comment instead of just removing it if it's not necessary?
Kevin
- [Qemu-devel] [PATCH] Add readonly flag to -drive command, Naphtali Sprei, 2009/10/12
- Re: [Qemu-devel] [PATCH] Add readonly flag to -drive command,
Kevin Wolf <=
- Re: [Qemu-devel] [PATCH] Add readonly flag to -drive command, Jamie Lokier, 2009/10/12
- Re: [Qemu-devel] [PATCH] Add readonly flag to -drive command, Kevin Wolf, 2009/10/12
- Re: [Qemu-devel] [PATCH] Add readonly flag to -drive command, Anthony Liguori, 2009/10/12
- Re: [Qemu-devel] [PATCH] Add readonly flag to -drive command, Jamie Lokier, 2009/10/12
- Re: [Qemu-devel] [PATCH] Add readonly flag to -drive command, Michael Tokarev, 2009/10/12
- Re: [Qemu-devel] [PATCH] Add readonly flag to -drive command, Kevin Wolf, 2009/10/13
- Re: [Qemu-devel] [PATCH] Add readonly flag to -drive command, Anthony Liguori, 2009/10/12