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Re: [Qemu-block] [Qemu-devel] [PATCH for-2.12 v5] file-posix: specify ex

From: Eric Blake
Subject: Re: [Qemu-block] [Qemu-devel] [PATCH for-2.12 v5] file-posix: specify expected filetypes
Date: Wed, 21 Mar 2018 15:26:29 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.6.0

On 03/21/2018 03:01 PM, John Snow wrote:
Adjust each caller of raw_open_common to specify if they are expecting
host and character devices or not. Tighten expectations of file types upon
open in the common code and refuse types that are not expected.

This has two effects:

(1) Character and block devices are now considered deprecated for the
     'file' driver, which expects only S_IFREG, and

Which may have interesting effects on v2v's attempt to use qemu-img on /dev/null as a quick feature probe of qemu-img...

but we may want to special-case that one in a separate patch.

(2) no file-posix driver (file, host_cdrom, or host_device) can open
     directories now.

I don't think there's a legitimate reason to open directories as if
they were files. This prevents QEMU from opening and attempting to probe
a directory inode, which can break in exciting ways. One of those ways
is lseek on ext4/xfs, which will return 0x7fffffffffffffff as the file
size instead of EISDIR. This can coax QEMU into responding with a
confusing "file too big" instead of "Hey, that's not a file".

See: https://bugs.launchpad.net/qemu/+bug/1739304/
Signed-off-by: John Snow <address@hidden>

v5: rebase for 2.12.0-rc0

Still makes sense as a 2.12 bugfix.

Reviewed-by: Eric Blake <address@hidden>

Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

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