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Michael Kelley 4a7d64d385 scsi: storvsc: Handle BlockSize change in Hyper-V VHD/VHDX file 
[ Upstream commit 11d9874c42 ]

Hyper-V uses a VHD or VHDX file on the host as the underlying storage for a
virtual disk.  The VHD/VHDX file format is a sparse format where real disk
space on the host is assigned in chunks that the VHD/VHDX file format calls
the BlockSize.  This BlockSize is not to be confused with the 512-byte (or
4096-byte) sector size of the underlying storage device.  The default block
size for a new VHD/VHDX file is 32 Mbytes.  When a guest VM touches any
disk space within a 32 Mbyte chunk of the VHD/VHDX file, Hyper-V allocates
32 Mbytes of real disk space for that section of the VHD/VHDX. Similarly,
if a discard operation is done that covers an entire 32 Mbyte chunk,
Hyper-V will free the real disk space for that portion of the VHD/VHDX.
This BlockSize is surfaced in Linux as the "discard_granularity" in
/sys/block/sd<x>/queue, which makes sense.

Hyper-V also has differencing disks that can overlay a VHD/VHDX file to
capture changes to the VHD/VHDX while preserving the original VHD/VHDX.
One example of this differencing functionality is for VM snapshots.  When a
snapshot is created, a differencing disk is created.  If the snapshot is
rolled back, Hyper-V can just delete the differencing disk, and the VM will
see the original disk contents at the time the snapshot was taken.
Differencing disks are used in other scenarios as well.

The BlockSize for a differencing disk defaults to 2 Mbytes, not 32 Mbytes.
The smaller default is used because changes to differencing disks are
typically scattered all over, and Hyper-V doesn't want to allocate 32
Mbytes of real disk space for a stray write here or there.  The smaller
BlockSize provides more efficient use of real disk space.

When a differencing disk is added to a VHD/VHDX, Hyper-V reports
UNIT_ATTENTION with a sense code indicating "Operating parameters have
changed", because the value of discard_granularity should be changed to 2
Mbytes. When the differencing disk is removed, discard_granularity should
be changed back to 32 Mbytes.  However, current code simply reports a
message from scsi_report_sense() and the value of
/sys/block/sd<x>/queue/discard_granularity is not updated. The message
isn't very actionable by a sysadmin.

Fix this by having the storvsc driver check for the sense code indicating
that the underly VHD/VHDX block size has changed, and do a rescan of the
device to pick up the new discard_granularity.  With this change the entire
transition to/from differencing disks is handled automatically and
transparently, with no confusing messages being output.

Link: https://lore.kernel.org/r/1677516514-86060-1-git-send-email-mikelley@microsoft.com
Signed-off-by: Michael Kelley <mikelley@microsoft.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
History 2023-03-30 12:49:19 +02:00
arch m68k: Only force 030 bus error if PC not in exception table 2023-03-30 12:49:17 +02:00
block block: do not reverse request order when flushing plug list 2023-03-22 13:33:46 +01:00
certs certs: Fix build error when PKCS#11 URI contains semicolon 2023-02-09 11:28:11 +01:00
crypto crypto: rsa-pkcs1pad - Use akcipher_request_complete 2023-03-10 09:33:03 +01:00
Documentation docs: Correct missing "d_" prefix for dentry_operations member d_weak_revalidate 2023-03-22 13:33:40 +01:00
drivers scsi: storvsc: Handle BlockSize change in Hyper-V VHD/VHDX file 2023-03-30 12:49:19 +02:00
fs smb3: fix unusable share after force unmount failure 2023-03-30 12:49:14 +02:00
include entry: Fix noinstr warning in __enter_from_user_mode() 2023-03-30 12:49:13 +02:00
init gcc: disable -Warray-bounds for gcc-11 too 2023-01-14 10:33:43 +01:00
io_uring io_uring/msg_ring: let target know allocated index 2023-03-22 13:34:06 +01:00
ipc ipc: fix memory leak in init_mqueue_fs() 2022-12-31 13:32:01 +01:00
kernel entry/rcu: Check TIF_RESCHED _after_ delayed RCU wake-up 2023-03-30 12:49:13 +02:00
lib sbitmap: Try each queue to wake up at least one waiter 2023-03-10 09:34:34 +01:00
LICENSES LICENSES/LGPL-2.1: Add LGPL-2.1-or-later as valid identifiers 2021-12-16 14:33:10 +01:00
mm mm: teach mincore_hugetlb about pte markers 2023-03-22 13:34:03 +01:00
net Bluetooth: HCI: Fix global-out-of-bounds 2023-03-30 12:49:12 +02:00
rust rust: print: avoid evaluating arguments in pr_* macros in unsafe blocks 2023-02-06 08:06:34 +01:00
samples ftrace: Export ftrace_free_filter() to modules 2023-02-01 08:34:37 +01:00
scripts kconfig: Update config changed flag before calling callback 2023-03-22 13:33:52 +01:00
security keys: Do not cache key in task struct if key is requested from kernel thread 2023-03-30 12:49:07 +02:00
sound ASoC: amd: yc: Add DMI entries to support HP OMEN 16-n0xxx (8A43) 2023-03-30 12:49:15 +02:00
tools selftests/bpf: check that modifier resolves after pointer 2023-03-30 12:49:17 +02:00
usr usr/gen_init_cpio.c: remove unnecessary -1 values from int file 2022-10-03 14:21:44 -07:00
virt KVM: Register /dev/kvm as the _very_ last thing during initialization 2023-03-10 09:34:11 +01:00
.clang-format inet: ping: use hlist_nulls rcu iterator during lookup 2022-12-01 12:42:46 +01:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore get_maintainer: add Alan to .get_maintainer.ignore 2022-08-20 15:17:44 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore Kbuild: add Rust support 2022-09-28 09:02:20 +02:00
.mailmap 9 hotfixes. 6 for MM, 3 for other areas. Four of these patches address 2022-12-10 17:10:52 -08:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Remove Michal Marek from Kbuild maintainers 2022-11-16 14:53:00 +09:00
Kbuild Kbuild updates for v6.1 2022-10-10 12:00:45 -07:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS audit: update the mailing list in MAINTAINERS 2023-02-25 11:25:42 +01:00
Makefile Linux 6.1.21 2023-03-22 13:34:07 +01:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.