Alberto García

O Grove (Spain)

One of the founding members of Igalia, Alberto loves computing since he got his first ZX Spectrum in the early nineties.

Latest Updates

Alberto García 16/11/2017

“Improving the performance of the qcow2 format” at KVM Forum 2017

I was in Prague last month for the 2017 edition of the KVM Forum. There I gave a talk about some of the work that I’ve been doing this year to improve the qcow2 file format used by QEMU for storing disk images. The focus of my work is to make qcow2...

Alberto García 08/02/2017

QEMU and the qcow2 metadata checks

When choosing a disk image format for your virtual machine one of the factors to take into considerations is its I/O performance. In this post I’ll talk a bit about the internals of qcow2 and about one of the aspects that can affect its performance...

Alberto García 24/05/2016

I/O bursts with QEMU 2.6

QEMU 2.6 was released a few days ago. One new feature that I have been working on is the new way to configure I/O limits in disk drives to allow bursts and increase the responsiveness of the virtual machine. In this post I’ll try to explain how it...

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qcow2: Add iotest for an empty refcount table

qcow2: Add iotest for an empty refcount table This patch adds a simple iotest in which we try to write to an image with an empty refcount table (i.e. with all entries set to 0). This scenario was already handled by the existing consistency checks, but...

Alberto García14/11/2017

qcow2: Add iotest for an image with header.refcount_table_offset == 0

qcow2: Add iotest for an image with header.refcount_table_offset == 0 This patch adds a simple iotest in which we try to write to an image with the refcount table offset set to 0. This scenario was already handled by the existing consistency...

Alberto García14/11/2017

qcow2: Don't open images with header.refcount_table_clusters == 0

qcow2: Don't open images with header.refcount_table_clusters == 0 qcow2_do_open() is checking that header.refcount_table_clusters is not too large, but it doesn't check that it's greater than zero. Apart from the fact that an image like...

Alberto García14/11/2017

qcow2: Prevent allocating compressed clusters at offset 0

qcow2: Prevent allocating compressed clusters at offset 0 If the refcount data is corrupted then we can end up trying to allocate a new compressed cluster at offset 0 in the image, triggering an assertion in qcow2_alloc_bytes() that would crash QEMU: ...

Alberto García14/11/2017

qcow2: Prevent allocating L2 tables at offset 0

qcow2: Prevent allocating L2 tables at offset 0 If the refcount data is corrupted then we can end up trying to allocate a new L2 table at offset 0 in the image, triggering an assertion in the qcow2 cache that would crash QEMU: ...

Alberto García14/11/2017