Linux kernel ============ The Linux kernel is the core of any Linux operating system. It manages hardware, system resources, and provides the fundamental services for all other software. Quick Start ----------- * Report a bug: See Documentation/admin-guide/reporting-issues.rst * Get the latest kernel: https://kernel.org * Build the kernel: See Documentation/admin-guide/quickly-build-trimmed-linux.rst * Join the community: https://lore.kernel.org/ Essential Documentation ----------------------- All users should be familiar with: * Building requirements: Documentation/process/changes.rst * Code of Conduct: Documentation/process/code-of-conduct.rst * License: See COPYING Documentation can be built with make htmldocs or viewed online at: https://www.kernel.org/doc/html/latest/ Who Are You? ============ Find your role below: * New Kernel Developer - Getting started with kernel development * Academic Researcher - Studying kernel internals and architecture * Security Expert - Hardening and vulnerability analysis * Backport/Maintenance Engineer - Maintaining stable kernels * System Administrator - Configuring and troubleshooting * Maintainer - Leading subsystems and reviewing patches * Hardware Vendor - Writing drivers for new hardware * Distribution Maintainer - Packaging kernels for distros * AI Coding Assistant - LLMs and AI-powered development tools For Specific Users ================== New Kernel Developer -------------------- Welcome! Start your kernel development journey here: * Getting Started: Documentation/process/development-process.rst * Your First Patch: Documentation/process/submitting-patches.rst * Coding Style: Documentation/process/coding-style.rst * Build System: Documentation/kbuild/index.rst * Development Tools: Documentation/dev-tools/index.rst * Kernel Hacking Guide: Documentation/kernel-hacking/hacking.rst * Core APIs: Documentation/core-api/index.rst Academic Researcher ------------------- Explore the kernel's architecture and internals: * Researcher Guidelines: Documentation/process/researcher-guidelines.rst * Memory Management: Documentation/mm/index.rst * Scheduler: Documentation/scheduler/index.rst * Networking Stack: Documentation/networking/index.rst * Filesystems: Documentation/filesystems/index.rst * RCU (Read-Copy Update): Documentation/RCU/index.rst * Locking Primitives: Documentation/locking/index.rst * Power Management: Documentation/power/index.rst Security Expert --------------- Security documentation and hardening guides: * Security Documentation: Documentation/security/index.rst * LSM Development: Documentation/security/lsm-development.rst * Self Protection: Documentation/security/self-protection.rst * Reporting Vulnerabilities: Documentation/process/security-bugs.rst * CVE Procedures: Documentation/process/cve.rst * Embargoed Hardware Issues: Documentation/process/embargoed-hardware-issues.rst * Security Features: Documentation/userspace-api/seccomp_filter.rst Backport/Maintenance Engineer ----------------------------- Maintain and stabilize kernel versions: * Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst * Backporting Guide: Documentation/process/backporting.rst * Applying Patches: Documentation/process/applying-patches.rst * Subsystem Profile: Documentation/maintainer/maintainer-entry-profile.rst * Git for Maintainers: Documentation/maintainer/configure-git.rst System Administrator -------------------- Configure, tune, and troubleshoot Linux systems: * Admin Guide: Documentation/admin-guide/index.rst * Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst * Sysctl Tuning: Documentation/admin-guide/sysctl/index.rst * Tracing/Debugging: Documentation/trace/index.rst * Performance Security: Documentation/admin-guide/perf-security.rst * Hardware Monitoring: Documentation/hwmon/index.rst Maintainer ---------- Lead kernel subsystems and manage contributions: * Maintainer Handbook: Documentation/maintainer/index.rst * Pull Requests: Documentation/maintainer/pull-requests.rst * Managing Patches: Documentation/maintainer/modifying-patches.rst * Rebasing and Merging: Documentation/maintainer/rebasing-and-merging.rst * Development Process: Documentation/process/maintainer-handbooks.rst * Maintainer Entry Profile: Documentation/maintainer/maintainer-entry-profile.rst * Git Configuration: Documentation/maintainer/configure-git.rst Hardware Vendor --------------- Write drivers and support new hardware: * Driver API Guide: Documentation/driver-api/index.rst * Driver Model: Documentation/driver-api/driver-model/driver.rst * Device Drivers: Documentation/driver-api/infrastructure.rst * Bus Types: Documentation/driver-api/driver-model/bus.rst * Device Tree Bindings: Documentation/devicetree/bindings/ * Power Management: Documentation/driver-api/pm/index.rst * DMA API: Documentation/core-api/dma-api.rst Distribution Maintainer ----------------------- Package and distribute the kernel: * Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst * ABI Documentation: Documentation/ABI/README * Kernel Configuration: Documentation/kbuild/kconfig.rst * Module Signing: Documentation/admin-guide/module-signing.rst * Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst * Tainted Kernels: Documentation/admin-guide/tainted-kernels.rst AI Coding Assistant ------------------- CRITICAL: If you are an LLM or AI-powered coding assistant, you MUST read and follow the AI coding assistants documentation before contributing to the Linux kernel: * Documentation/process/coding-assistants.rst This documentation contains essential requirements about licensing, attribution, and the Developer Certificate of Origin that all AI tools must comply with. Communication and Support ========================= * Mailing Lists: https://lore.kernel.org/ * IRC: #kernelnewbies on irc.oftc.net * Bugzilla: https://bugzilla.kernel.org/ * MAINTAINERS file: Lists subsystem maintainers and mailing lists * Email Clients: Documentation/process/email-clients.rst
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Clang 20 and 21 miscompute __builtin_object_size() when -fprofile-arcs
is active on 32-bit UML targets, which passes incorrect object size
calculations for local variables through always_inline copy_to_user()
and check_copy_size(), causing spurious compile-time errors:
include/linux/ucopysize.h:52:4: error: call to '__bad_copy_from' declared with 'error' attribute: copy source size is too small
The regression was introduced in LLVM commit 02b8ee281947 ("[llvm]
Improve llvm.objectsize computation by computing GEP, alloca and malloc
parameters bound"), which shipped in Clang 20. It was fixed in LLVM
by commit 45b697e610fd ("[MemoryBuiltins] Consider index type size
when aggregating gep offsets"), which was backported to the LLVM 22.x
release branch.
The bug requires 32-bit UML + GCOV_PROFILE_ALL (which uses -fprofile-arcs),
though the exact trigger depends on optimizer decisions influenced by other
enabled configs.
Prevent the bad combination by disabling UML's ARCH_HAS_GCOV_PROFILE_ALL
on 32-bit when using Clang 20.x or 21.x.
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202604030531.O6FveVgn-lkp@intel.com/
Suggested-by: Nathan Chancellor <nathan@kernel.org>
Assisted-by: Claude:claude-opus-4-6[1m]
Signed-off-by: Kees Cook <kees@kernel.org>
Link: https://patch.msgid.link/20260409052038.make.995-kees@kernel.org
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Building ARCH=um on glibc >= 2.43 fails:
arch/um/drivers/cow_user.c: error: implicit declaration of
function 'strrchr' [-Wimplicit-function-declaration]
glibc 2.43's C23 const-preserving strrchr() macro does not survive
UML's global -Dstrrchr=kernel_strrchr remap from arch/um/Makefile.
Call kernel_strrchr() directly in cow_user.c so the source no longer
depends on the -D rewrite.
Fixes: 2c51a4bc0233 ("um: fix strrchr() problems")
Suggested-by: Johannes Berg <johannes@sipsolutions.net>
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-4-6
Assisted-by: Codex:gpt-5-4
Signed-off-by: Michael Bommarito <michael.bommarito@gmail.com>
Link: https://patch.msgid.link/20260408070102.2325572-1-michael.bommarito@gmail.com
[remove unnecessary 'extern']
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Replace the deprecated[1] strncpy() with strnlen() on the source
followed by memcpy_and_pad().
This function is a chunk callback for UML's strncpy_from_user()
implementation, called by buffer_op() to process userspace memory one
page at a time. The source is a kernel-mapped userspace address that
is not guaranteed to be NUL-terminated; "len" bounds how many bytes
to read from it.
By measuring the source string length first with strnlen(), we avoid
reading past the NUL terminator in the source. memcpy_and_pad() then
copies the string content and zero-fills the remainder of the chunk,
preserving the original strncpy() behavior exactly: copy up to the
first NUL, then pad with zeros to the full length.
strtomem_pad() would be the idiomatic helper for this strnlen() +
memcpy_and_pad() pattern, but it requires a compile-time-determinable
destination size (via ARRAY_SIZE()). Here the destination is a char *
into a caller-provided buffer and the chunk length is a runtime value,
so the explicit two-step is necessary.
No behavioral change: the same bytes are written to the destination
(string content followed by zero padding), the pointer advances by
the same amount, and the NUL-found return condition is unchanged.
Link: https://github.com/KSPP/linux/issues/90 [1]
Signed-off-by: Kees Cook <kees@kernel.org>
Link: https://patch.msgid.link/20260323171713.work.839-kees@kernel.org
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
The generic vDSO installation logic used by 'make vdso_install' requires
that $(vdso-install-y) is defined by the top-level architecture Makefile
and that it contains a path relative to the root of the tree.
For UML neither of these is satisfied.
Move the definition of $(vdso-install-y) to a place which is included by
the arch/um/Makefile and use the full relative path.
Fixes: f1c2bb8b9964 ("um: implement a x86_64 vDSO")
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Link: https://patch.msgid.link/20260318-um-vdso-install-v1-1-26a4ca5c4210@weissschuh.net
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
The CONFIG_FRAME_WARN=1024 setting in x86_64_defconfig originates
from arch/um/defconfig, which was split into i386_defconfig and
x86_64_defconfig by commit e40f04d040c6 ("arch/um: make it work
with defconfig and x86_64"). Currently, it's even smaller than the
default on 32bit (i.e., 1280). It's no longer suitable for 64bit.
Building with x86_64_defconfig triggers the following warning:
lib/maple_tree.c: In function ‘mas_wr_bnode’:
lib/maple_tree.c:3740:1: warning: the frame size of 1056 bytes is larger than 1024 bytes [-Wframe-larger-than=]
3740 | }
| ^
Since we have a larger CONFIG_KERNEL_STACK_ORDER on 64bit (twice
that of 32bit) by default, we could increase CONFIG_FRAME_WARN
accordingly. Let's remove the CONFIG_FRAME_WARN=1024 setting from
x86_64_defconfig and just use the default value (2048 for 64bit)
defined in lib/Kconfig.debug, as we do for 32bit.
Signed-off-by: Tiwei Bie <tiwei.btw@antgroup.com>
Link: https://patch.msgid.link/20260308060406.2772832-1-tiwei.btw@antgroup.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
The pte_read() and pte_exec() helpers are only used during the TLB
sync to determine the read/exec permissions for mmap. However, for
kernel mappings, they will always return 0. This leads to kern_map()
having to unconditionally set the exec flag to 1 and the read flag
unexpectedly always being 0. Remove the unnecessary check for the
_PAGE_USER bit in these helpers to ensure that the kernel mapping
permissions can be correctly determined.
Signed-off-by: Tiwei Bie <tiwei.btw@antgroup.com>
Link: https://patch.msgid.link/20260302235224.1915380-3-tiwei.btw@antgroup.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
During the TLB sync, we need to traverse and modify the page table,
so we should hold the page table lock. Since full SMP support for
threads within the same process is still missing, let's disable the
split page table lock for simplicity.
Fixes: 1e4ee5135d81 ("um: Add initial SMP support")
Signed-off-by: Tiwei Bie <tiwei.btw@antgroup.com>
Link: https://patch.msgid.link/20260302235224.1915380-2-tiwei.btw@antgroup.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Repair all kernel-doc warnings in um_timetravel.h:
- add one enum description
- mark "reserve" as private
- use a leading '@' on current_time
Warning: include/uapi/linux/um_timetravel.h:59 Enum value
'UM_TIMETRAVEL_SHARED_MAX_FDS' not described in enum
'um_timetravel_shared_mem_fds'
Warning: include/uapi/linux/um_timetravel.h:245 union member 'reserve'
not described in 'um_timetravel_schedshm_client'
Warning: include/uapi/linux/um_timetravel.h:288 struct member
'current_time' not described in 'um_timetravel_schedshm'
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Link: https://patch.msgid.link/20260226221112.1042008-1-rdunlap@infradead.org
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
mcontext.c includes both <sys/ucontext.h> and <asm/sigcontext.h>.
With musl libc, this causes a struct sigcontext redefinition error:
<sys/ucontext.h> pulls in musl's <bits/signal.h>, which defines
struct sigcontext directly. The kernel's <asm/sigcontext.h> then
provides a second, conflicting definition of the same struct.
With glibc this does not conflict because glibc's signal headers
source their struct sigcontext from the kernel's own UAPI headers,
so the include guard in <asm/sigcontext.h> makes the second
inclusion a no-op.
mcontext.c does not actually use struct sigcontext by name -- it
only needs the FP-state types (_fpstate, _xstate, etc.) that are
defined in <asm/sigcontext.h> independently of the sigcontext
struct.
Temporarily rename sigcontext to __kernel_sigcontext during the
inclusion of <asm/sigcontext.h> so that the kernel's definition
does not collide with musl's. The #undef restores normal name
resolution immediately afterward.
No functional change with glibc; fixes the build with musl.
Signed-off-by: Marcel W. Wysocki <maci.stgn@gmail.com>
Link: https://patch.msgid.link/20260215142803.1455757-2-maci.stgn@gmail.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
The UML stub takes the address of CMSG_DATA(fd_msg):
fd_map = (void *)&CMSG_DATA(fd_msg);
CMSG_DATA() is specified by POSIX to return unsigned char *. Taking
its address is semantically wrong -- the intent is to get a pointer
to the control message data, which is exactly what CMSG_DATA()
already returns.
This happens to compile with glibc because glibc's primary
CMSG_DATA definition accesses a flexible array member:
#define CMSG_DATA(cmsg) ((cmsg)->__cmsg_data)
An array lvalue can have its address taken, and &array yields the
same address as array. However, glibc also has an alternative
definition that uses pointer arithmetic (returning an rvalue), and
musl's definition always uses pointer arithmetic:
/* musl */
#define CMSG_DATA(cmsg) \
((unsigned char *)(((struct cmsghdr *)(cmsg)) + 1))
Taking the address of an rvalue is a hard error in C, so the
current code fails to compile with musl libc.
Remove the erroneous & operator. The resulting code is correct
regardless of the CMSG_DATA implementation -- it simply assigns the
data pointer, which is what the subsequent code (fd_map[--num_fds])
expects.
No functional change with glibc; fixes the build with musl.
Signed-off-by: Marcel W. Wysocki <maci.stgn@gmail.com>
Link: https://patch.msgid.link/20260215142803.1455757-1-maci.stgn@gmail.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Pull SCSI fixes from James Bottomley:
"The one core change is a re-roll of the tag allocation fix from the
last pull request that uses the correct goto to unroll all the
allocations. The remianing fixes are all small ones in drivers"
* tag 'scsi-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/jejb/scsi:
scsi: hisi_sas: Fix NULL pointer exception during user_scan()
scsi: qla2xxx: Completely fix fcport double free
scsi: ufs: core: Fix SError in ufshcd_rtc_work() during UFS suspend
scsi: core: Fix error handling for scsi_alloc_sdev()
Pull probes fixes from Masami Hiramatsu:
- Avoid crash when rmmod/insmod after ftrace killed
This fixes a kernel crash caused by kprobes on the symbol in a module
which is unloaded after ftrace_kill() is called.
- Remove unneeded warnings from __arm_kprobe_ftrace()
Remove unneeded WARN messages which can be triggered if the kprobe is
using ftrace and it fails to enable the ftrace. Since kprobes
correctly handle such failure, we don't need to warn it.
* tag 'probes-fixes-v7.0-rc3' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace:
kprobes: Remove unneeded warnings from __arm_kprobe_ftrace()
kprobes: avoid crash when rmmod/insmod after ftrace killed
user_scan() invokes updated sas_user_scan() for channel 0, and if
successful, iteratively scans remaining channels (1 to shost->max_channel)
via scsi_scan_host_selected() in commit 37c4e72b0651 ("scsi: Fix
sas_user_scan() to handle wildcard and multi-channel scans"). However,
hisi_sas supports only one channel, and the current value of max_channel is
1. sas_user_scan() for channel 1 will trigger the following NULL pointer
exception:
[ 441.554662] Unable to handle kernel NULL pointer dereference at virtual address 00000000000008b0
[ 441.554699] Mem abort info:
[ 441.554710] ESR = 0x0000000096000004
[ 441.554718] EC = 0x25: DABT (current EL), IL = 32 bits
[ 441.554723] SET = 0, FnV = 0
[ 441.554726] EA = 0, S1PTW = 0
[ 441.554730] FSC = 0x04: level 0 translation fault
[ 441.554735] Data abort info:
[ 441.554737] ISV = 0, ISS = 0x00000004, ISS2 = 0x00000000
[ 441.554742] CM = 0, WnR = 0, TnD = 0, TagAccess = 0
[ 441.554747] GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0
[ 441.554752] user pgtable: 4k pages, 48-bit VAs, pgdp=00000828377a6000
[ 441.554757] [00000000000008b0] pgd=0000000000000000, p4d=0000000000000000
[ 441.554769] Internal error: Oops: 0000000096000004 [#1] SMP
[ 441.629589] Modules linked in: arm_spe_pmu arm_smmuv3_pmu tpm_tis_spi hisi_uncore_sllc_pmu hisi_uncore_pa_pmu hisi_uncore_l3c_pmu hisi_uncore_hha_pmu hisi_uncore_ddrc_pmu hisi_uncore_cpa_pmu hns3_pmu hisi_ptt hisi_pcie_pmu tpm_tis_core spidev spi_hisi_sfc_v3xx hisi_uncore_pmu spi_dw_mmio fuse hclge hclge_common hisi_sec2 hisi_hpre hisi_zip hisi_qm hns3 hisi_sas_v3_hw sm3_ce sbsa_gwdt hnae3 hisi_sas_main uacce hisi_dma i2c_hisi dm_mirror dm_region_hash dm_log dm_mod
[ 441.670819] CPU: 46 UID: 0 PID: 6994 Comm: bash Kdump: loaded Not tainted 7.0.0-rc2+ #84 PREEMPT
[ 441.691327] pstate: 81400009 (Nzcv daif +PAN -UAO -TCO +DIT -SSBS BTYPE=--)
[ 441.698277] pc : sas_find_dev_by_rphy+0x44/0x118
[ 441.702896] lr : sas_find_dev_by_rphy+0x3c/0x118
[ 441.707502] sp : ffff80009abbba40
[ 441.710805] x29: ffff80009abbba40 x28: ffff082819a40008 x27: ffff082810c37c08
[ 441.717930] x26: ffff082810c37c28 x25: ffff082819a40290 x24: ffff082810c37c00
[ 441.725054] x23: 0000000000000000 x22: 0000000000000001 x21: ffff082819a40000
[ 441.732179] x20: ffff082819a40290 x19: 0000000000000000 x18: 0000000000000020
[ 441.739304] x17: 0000000000000000 x16: ffffb5dad6bda690 x15: 00000000ffffffff
[ 441.746428] x14: ffff082814c3b26c x13: 00000000ffffffff x12: ffff082814c3b26a
[ 441.753553] x11: 00000000000000c0 x10: 000000000000003a x9 : ffffb5dad5ea94f4
[ 441.760678] x8 : 000000000000003a x7 : ffff80009abbbab0 x6 : 0000000000000030
[ 441.767802] x5 : 0000000000000000 x4 : 0000000000000000 x3 : 0000000000000000
[ 441.774926] x2 : ffff08280f35a300 x1 : ffffb5dad7127180 x0 : 0000000000000000
[ 441.782053] Call trace:
[ 441.784488] sas_find_dev_by_rphy+0x44/0x118 (P)
[ 441.789095] sas_target_alloc+0x24/0xb0
[ 441.792920] scsi_alloc_target+0x290/0x330
[ 441.797010] __scsi_scan_target+0x88/0x258
[ 441.801096] scsi_scan_channel+0x74/0xb8
[ 441.805008] scsi_scan_host_selected+0x170/0x188
[ 441.809615] sas_user_scan+0xfc/0x148
[ 441.813267] store_scan+0x10c/0x180
[ 441.816743] dev_attr_store+0x20/0x40
[ 441.820398] sysfs_kf_write+0x84/0xa8
[ 441.824054] kernfs_fop_write_iter+0x130/0x1c8
[ 441.828487] vfs_write+0x2c0/0x370
[ 441.831880] ksys_write+0x74/0x118
[ 441.835271] __arm64_sys_write+0x24/0x38
[ 441.839182] invoke_syscall+0x50/0x120
[ 441.842919] el0_svc_common.constprop.0+0xc8/0xf0
[ 441.847611] do_el0_svc+0x24/0x38
[ 441.850913] el0_svc+0x38/0x158
[ 441.854043] el0t_64_sync_handler+0xa0/0xe8
[ 441.858214] el0t_64_sync+0x1ac/0x1b0
[ 441.861865] Code: aa1303e0 97ff70a8 34ffff80 d10a4273 (f9445a75)
[ 441.867946] ---[ end trace 0000000000000000 ]---
Therefore, set max_channel to 0.
Fixes: e21fe3a52692 ("scsi: hisi_sas: add initialisation for v3 pci-based controller")
Signed-off-by: Xingui Yang <yangxingui@huawei.com>
Signed-off-by: Yihang Li <liyihang9@huawei.com>
Link: https://patch.msgid.link/20260305064039.4096775-1-liyihang9@huawei.com
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Pull bootconfig fixes from Masami Hiramatsu:
- fix off-by-one in xbc_verify_tree() unclosed brace error. This fixes
a wrong error place in unclosed brace error message
- check bounds before writing in __xbc_open_brace(). This fixes to
check the array index before setting array, so that the bootconfig
can support 16th-depth nested brace correctly
- fix snprintf truncation check in xbc_node_compose_key_after(). This
fixes to handle the return value of snprintf() correctly in case of
the return value == size
- Add bootconfig tests about braces Add test cases for checking error
position about unclosed brace and ensuring supporting 16th depth
nested braces correctly
* tag 'bootconfig-fixes-v7.0-rc3' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace:
bootconfig: Add bootconfig tests about braces
lib/bootconfig: fix snprintf truncation check in xbc_node_compose_key_after()
lib/bootconfig: check bounds before writing in __xbc_open_brace()
lib/bootconfig: fix off-by-one in xbc_verify_tree() unclosed brace error
Remove unneeded warnings for handled errors from __arm_kprobe_ftrace()
because all caller handled the error correctly.
Link: https://lore.kernel.org/all/177261531182.1312989.8737778408503961141.stgit@mhiramat.tok.corp.google.com/
Reported-by: Zw Tang <shicenci@gmail.com>
Closes: https://lore.kernel.org/all/CAPHJ_V+J6YDb_wX2nhXU6kh466Dt_nyDSas-1i_Y8s7tqY-Mzw@mail.gmail.com/
Fixes: 9c89bb8e3272 ("kprobes: treewide: Cleanup the error messages for kprobes")
Cc: stable@vger.kernel.org
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>