Re: [Qemu-devel] [Qemu-block] [PATCH 0/3] block/file-posix: File locking during creation

[Alberto Garcia <berto@igalia.com>]

On Sat 21 Apr 2018 12:09:10 AM CEST, Max Reitz wrote:
> Currently we do not take permissions on a file while it is being
> created.  That is a bit sad.  The simplest way to test this is the
> following:
>
>     $ qemu-img create -f qcow2 foo.qcow2 64M
>     Formatting 'foo.qcow2', fmt=qcow2 size=67108864 cluster_size=65536 lazy_refcounts=off refcount_bits=16
>     $ qemu-img convert -f qcow2 -O qcow2 foo.qcow2 foo.qcow2
>     qemu-img: foo.qcow2: error while converting qcow2: Failed to get "write" lock
>     Is another process using the image?
>     $ qemu-img info foo.qcow2
>     image: foo.qcow2
>     file format: raw
>     virtual size: 0 (0 bytes)
>     disk size: 0

Not quite the same problem, but here's another example of QEMU creating
an image before checking if it can be created:

$ qemu-img create -o cluster_size=2M -f qcow2 img.qcow2 7E
Formatting 'img.qcow2', fmt=qcow2 size=8070450532247928832 encryption=off cluster_size=2097152 lazy_refcounts=off refcount_bits=16
qemu-img: img.qcow2: The image size is too large for file format 'qcow2' (try using a larger cluster size)

$ qemu-img info img.qcow2 
image: img.qcow2
file format: qcow2
virtual size: 0 (0 bytes)
disk size: 6.0M
cluster_size: 2097152
Format specific information:
    compat: 1.1
    lazy refcounts: false
    refcount bits: 16
    corrupt: false

Berto