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Alexey Dobriyan 941baf6feb proc: give /proc/cmdline size
Most /proc files don't have length (in fstat sense).  This leads to
inefficiencies when reading such files with APIs commonly found in modern
programming languages.  They open file, then fstat descriptor, get st_size
== 0 and either assume file is empty or start reading without knowing
target size.

cat(1) does OK because it uses large enough buffer by default.  But naive
programs copy-pasted from SO aren't:

	let mut f = std::fs::File::open("/proc/cmdline").unwrap();
	let mut buf: Vec<u8> = Vec::new();
	f.read_to_end(&mut buf).unwrap();

will result in

	openat(AT_FDCWD, "/proc/cmdline", O_RDONLY|O_CLOEXEC) = 3
	statx(0, NULL, AT_STATX_SYNC_AS_STAT, STATX_ALL, NULL) = -1 EFAULT (Bad address)
	statx(3, "", AT_STATX_SYNC_AS_STAT|AT_EMPTY_PATH, STATX_ALL, {stx_mask=STATX_BASIC_STATS|STATX_MNT_ID, stx_attributes=0, stx_mode=S_IFREG|0444, stx_size=0, ...}) = 0
	lseek(3, 0, SEEK_CUR)                   = 0
	read(3, "BOOT_IMAGE=(hd3,gpt2)/vmlinuz-5.", 32) = 32
	read(3, "19.6-100.fc35.x86_64 root=/dev/m", 32) = 32
	read(3, "apper/fedora_localhost--live-roo"..., 64) = 64
	read(3, "ocalhost--live-swap rd.lvm.lv=fe"..., 128) = 116
	read(3, "", 12)

open/stat is OK, lseek looks silly but there are 3 unnecessary reads
because Rust starts with 32 bytes per Vec<u8> and grows from there.

In case of /proc/cmdline, the length is known precisely.

Make variables readonly while I'm at it.

P.S.: I tried to scp /proc/cpuinfo today and got empty file
	but this is separate story.

Link: https://lkml.kernel.org/r/YxoywlbM73JJN3r+@localhost.localdomain
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-11-18 13:55:07 -08:00
arch ARM: kexec: make machine_crash_nonpanic_core() static 2022-11-18 13:55:07 -08:00
block block-6.1-2022-11-05 2022-11-05 09:02:28 -07:00
certs
crypto
Documentation proc: report open files as size in stat() for /proc/pid/fd 2022-11-18 13:55:07 -08:00
drivers cxl fixes for 6.1-rc4 2022-11-06 13:09:52 -08:00
fs proc: give /proc/cmdline size 2022-11-18 13:55:07 -08:00
include proc: give /proc/cmdline size 2022-11-18 13:55:07 -08:00
init proc: give /proc/cmdline size 2022-11-18 13:55:07 -08:00
io_uring io_uring: unlock if __io_run_local_work locked inside 2022-10-27 09:52:12 -06:00
ipc ipc/msg.c: fix percpu_counter use after free 2022-10-28 13:37:22 -07:00
kernel kexec: replace crash_mem_range with range 2022-11-18 13:55:07 -08:00
lib llist: avoid extra memory read in llist_add_batch 2022-11-18 13:55:06 -08:00
LICENSES
mm mmap: fix remap_file_pages() regression 2022-10-28 13:37:23 -07:00
net Networking fixes for 6.1-rc4, including fixes from bluetooth and 2022-11-03 10:51:59 -07:00
rust
samples
scripts checkpatch: add warning for non-lore mailing list URLs 2022-11-18 13:55:07 -08:00
security lsm/stable-6.1 PR 20221031 2022-10-31 12:09:42 -07:00
sound ALSA: aoa: Fix I2S device accounting 2022-10-27 08:53:08 +02:00
tools cxl fixes for 6.1-rc4 2022-11-06 13:09:52 -08:00
usr
virt Merge tag 'kvmarm-fixes-6.1-3' of git://git.kernel.org/pub/scm/linux/kernel/git/kvmarm/kvmarm into HEAD 2022-11-06 03:30:49 -05:00
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MAINTAINERS MAINTAINERS: git://github -> https://github.com for linux-test-project 2022-11-18 13:55:06 -08:00
Makefile Linux 6.1-rc4 2022-11-06 15:07:11 -08:00
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.