linux-kernel - [PATCH 1/1] vmgenid: emit uevent with new generation ID

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Message-ID: <20240730094831.882166-2-bchalios@amazon.es>
Date: Tue, 30 Jul 2024 11:48:31 +0200
From: Babis Chalios <bchalios@...zon.es>
To: <tytso@....edu>, <Jason@...c4.com>, <linux-kernel@...r.kernel.org>
CC: <graf@...zon.de>, <mzxreary@...inter.de>, <xmarcalx@...zon.co.uk>,
	<gregkh@...uxfoundation.org>, Babis Chalios <bchalios@...zon.es>
Subject: [PATCH 1/1] vmgenid: emit uevent with new generation ID

There are many system services that need to be notified when the VM they
are running in is resumed from a snapshot. One example are network
managers which need to renew DHCP leases and/or re-create MAC addresses
for virtual interfaces. Other example are daemons that manage system
clocks which need reset upon snapshot resume.

Send a uevent notification to user space from the VMGenID driver when
we receive the ACPI notification about a new generation ID. This way, we
notify user space software about the VM cloning event and give it a
chance to adapt to the new environment.

Signed-off-by: Babis Chalios <bchalios@...zon.es>
---
 drivers/virt/vmgenid.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/virt/vmgenid.c b/drivers/virt/vmgenid.c
index 66135eac3abff..5410620a017f5 100644
--- a/drivers/virt/vmgenid.c
+++ b/drivers/virt/vmgenid.c
@@ -26,6 +26,7 @@ struct vmgenid_state {
 static void vmgenid_notify(struct device *device)
 {
 	struct vmgenid_state *state = device->driver_data;
+	char *envp[] = { "NEW_VMGENID=1", NULL };
 	u8 old_id[VMGENID_SIZE];

 	memcpy(old_id, state->this_id, sizeof(old_id));
@@ -33,6 +34,7 @@ static void vmgenid_notify(struct device *device)
 	if (!memcmp(old_id, state->this_id, sizeof(old_id)))
 		return;
 	add_vmfork_randomness(state->this_id, sizeof(state->this_id));
+	kobject_uevent_env(&device->kobj, KOBJ_CHANGE, envp);
 }

 static void setup_vmgenid_state(struct vmgenid_state *state, void *virt_addr)
-- 
2.34.1