linux-kernel - [PATCH V5 08/11] vfio/pci: Use bitfield for struct vfio_pci_core

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Message-Id: <cf34bf0499c889554a8105eeb18cc0ab673005be.1683740667.git.reinette.chatre@intel.com>
Date:   Thu, 11 May 2023 08:44:35 -0700
From:   Reinette Chatre <reinette.chatre@...el.com>
To:     jgg@...dia.com, yishaih@...dia.com,
        shameerali.kolothum.thodi@...wei.com, kevin.tian@...el.com,
        alex.williamson@...hat.com
Cc:     tglx@...utronix.de, darwi@...utronix.de, kvm@...r.kernel.org,
        dave.jiang@...el.com, jing2.liu@...el.com, ashok.raj@...el.com,
        fenghua.yu@...el.com, tom.zanussi@...ux.intel.com,
        reinette.chatre@...el.com, linux-kernel@...r.kernel.org
Subject: [PATCH V5 08/11] vfio/pci: Use bitfield for struct vfio_pci_core_device flags

struct vfio_pci_core_device contains eleven boolean flags.
Boolean flags clearly indicate their usage but space usage
starts to be a concern when there are many.

An upcoming change adds another boolean flag to
struct vfio_pci_core_device, thereby increasing the concern
that the boolean flags are consuming unnecessary space.

Transition the boolean flags to use bitfields. On a system that
uses one byte per boolean this reduces the space consumed
by existing flags from 11 bytes to 2 bytes with room for
a few more flags without increasing the structure's size.

Suggested-by: Jason Gunthorpe <jgg@...dia.com>
Signed-off-by: Reinette Chatre <reinette.chatre@...el.com>
Reviewed-by: Kevin Tian <kevin.tian@...el.com>
---
Changes since V4:
- Add Kevin's Reviewed-by tag. (Kevin)

Changes since V3:
- New patch. (Jason)

 include/linux/vfio_pci_core.h | 22 +++++++++++-----------
 1 file changed, 11 insertions(+), 11 deletions(-)

diff --git a/include/linux/vfio_pci_core.h b/include/linux/vfio_pci_core.h
index 148fd1ae6c1c..adb47e2914d7 100644
--- a/include/linux/vfio_pci_core.h
+++ b/include/linux/vfio_pci_core.h
@@ -68,17 +68,17 @@ struct vfio_pci_core_device {
 	u16			msix_size;
 	u32			msix_offset;
 	u32			rbar[7];
-	bool			pci_2_3;
-	bool			virq_disabled;
-	bool			reset_works;
-	bool			extended_caps;
-	bool			bardirty;
-	bool			has_vga;
-	bool			needs_reset;
-	bool			nointx;
-	bool			needs_pm_restore;
-	bool			pm_intx_masked;
-	bool			pm_runtime_engaged;
+	bool			pci_2_3:1;
+	bool			virq_disabled:1;
+	bool			reset_works:1;
+	bool			extended_caps:1;
+	bool			bardirty:1;
+	bool			has_vga:1;
+	bool			needs_reset:1;
+	bool			nointx:1;
+	bool			needs_pm_restore:1;
+	bool			pm_intx_masked:1;
+	bool			pm_runtime_engaged:1;
 	struct pci_saved_state	*pci_saved_state;
 	struct pci_saved_state	*pm_save;
 	int			ioeventfds_nr;
-- 
2.34.1