Messages in this thread | | | Date | Wed, 3 Aug 2022 17:28:08 +0200 | From | Greg KH <> | Subject | Re: [PATCH 2/2] virt: vmgenid: add support for generation counter |
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On Wed, Aug 03, 2022 at 05:21:27PM +0200, bchalios@amazon.es wrote: > From: Babis Chalios <bchalios@amazon.es> > > VM Generation ID provides a means of reseeding kernel's RNG using a > 128-bit UUID when a VM fork occurs, thus avoiding issues running > multiple VMs with the exact same RNG state. However, user-space > applications, such as user-space PRNGs and applications that maintain > world-unique data, need a mechanism to handle VM fork events as well. > > To handle the user-space use-case, this: <url> qemu patch extends > Microsoft's original vmgenid specification adding an extra page which > holds a single 32-bit generation counter, which increases every time a > VM gets restored from a snapshot. > > This patch exposes the generation counter through a character device > (`/dev/vmgenid`) that provides a `read` and `mmap` interface, for > user-space applications to consume. Userspace applications should read > this value before starting a transaction involving cached random bits > and ensure that it has not changed while committing the transaction. > > It can be used from qemu using the `-device vmgenid,guid=auto,genctr=42` > parameter to start a VM with a generation counter with value 42. > Reading 4 bytes from `/dev/vmgenid` will return the value 42. Next, use > `savevm my_snapshot` in the monitor to snapshot the VM. Now, start > another VM using `-device vmgenid,guid=auto,genctr=43 -loadvm > my_snapshot`. Reading now from `/dev/vmgenid` will return 43. > > Signed-off-by: Babis Chalios <bchalios@amazon.es> > --- > Documentation/virt/vmgenid.rst | 120 +++++++++++++++++++++++++++++++++ > drivers/virt/vmgenid.c | 103 +++++++++++++++++++++++++++- > 2 files changed, 221 insertions(+), 2 deletions(-) > create mode 100644 Documentation/virt/vmgenid.rst > > diff --git a/Documentation/virt/vmgenid.rst b/Documentation/virt/vmgenid.rst > new file mode 100644 > index 000000000..61c29e4a7 > --- /dev/null > +++ b/Documentation/virt/vmgenid.rst > @@ -0,0 +1,120 @@ > +.. SPDX-License-Identifier: GPL-2.0 > + > +======= > +VMGENID > +=======
<snip>
This file is now just floating in the directory, not tied to anything, so auto-generation of the documentation will not pick it up or link to it, right?
So, why does this have to be a separate file at all? Why not put this in the .c file and pull it straight from there so that it keeps in sync with the code easier?
thanks,
greg k-h
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