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Re: [Qemu-devel] [PATCH 4/5] block: cow - used QEMU_PACKED for on-disk s
From: |
Richard Henderson |
Subject: |
Re: [Qemu-devel] [PATCH 4/5] block: cow - used QEMU_PACKED for on-disk structures |
Date: |
Wed, 25 Sep 2013 12:39:48 -0700 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130805 Thunderbird/17.0.8 |
On 09/25/2013 12:01 PM, Jeff Cody wrote:
> It is from UML, right? Is there an official spec that is still around
> (most of the links I have found suffer from link rot)? The closest I
> could find to a spec were old UML patches for x86_64 that cleaned up
> some data types, so that the following was defined:
>
> struct cow_header_v2 {
>
> __u32 magic;
> __u32 version;
> char backing_file[PATH_LEN_V2];
> time_t mtime;
> __u64 size;
> int sectorsize;
> };
>
> That remains ambiguous, although given the era I suppose it could be
> argued that 32-bit architecture and alignment is assumed. But if this
> is the original spec, then it seems like a non-portable one.
Indeed. Not just the potential padding there, but of course
the size of time_t varies between hosts. And since we use
an int32_t not time_t, we're not even necessarily compatible
with UML.
r~
- [Qemu-devel] [PATCH 0/5] block: use QEMU_PACKED for on-disk structures, Jeff Cody, 2013/09/19
- [Qemu-devel] [PATCH 1/5] block: vdi - use QEMU_PACKED for on-disk structures, Jeff Cody, 2013/09/19
- [Qemu-devel] [PATCH 2/5] block: vpc - use QEMU_PACKED for on-disk structures, Jeff Cody, 2013/09/19
- [Qemu-devel] [PATCH 4/5] block: cow - used QEMU_PACKED for on-disk structures, Jeff Cody, 2013/09/19
- Re: [Qemu-devel] [PATCH 4/5] block: cow - used QEMU_PACKED for on-disk structures, Richard Henderson, 2013/09/19
- Re: [Qemu-devel] [PATCH 4/5] block: cow - used QEMU_PACKED for on-disk structures, Jeff Cody, 2013/09/20
- Re: [Qemu-devel] [PATCH 4/5] block: cow - used QEMU_PACKED for on-disk structures, Markus Armbruster, 2013/09/20
- Re: [Qemu-devel] [PATCH 4/5] block: cow - used QEMU_PACKED for on-disk structures, Jeff Cody, 2013/09/25
- Re: [Qemu-devel] [PATCH 4/5] block: cow - used QEMU_PACKED for on-disk structures, Kevin Wolf, 2013/09/25
- Re: [Qemu-devel] [PATCH 4/5] block: cow - used QEMU_PACKED for on-disk structures, Jeff Cody, 2013/09/25
- Re: [Qemu-devel] [PATCH 4/5] block: cow - used QEMU_PACKED for on-disk structures,
Richard Henderson <=
[Qemu-devel] [PATCH 3/5] block: qcow2 - used QEMU_PACKED for on-disk structures, Jeff Cody, 2013/09/19
[Qemu-devel] [PATCH 5/5] block: qed - use QEMU_PACKED for on-disk structures, Jeff Cody, 2013/09/19
Re: [Qemu-devel] [PATCH 0/5] block: use QEMU_PACKED for on-disk structures, Kevin Wolf, 2013/09/20