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| author | Alexey Dobriyan <adobriyan@gmail.com> | 2022-09-08 21:21:54 +0300 |
|---|---|---|
| committer | Andrew Morton <akpm@linux-foundation.org> | 2022-11-18 13:55:07 -0800 |
| commit | 941baf6febaa88c057192084ca280d976c7c7239 (patch) | |
| tree | b38ce270a9f8c6c5f6f2f157a3b174d41d464687 /include/linux/init.h | |
| parent | 9b71f79f6e349251e529ef25f2d3bf8aa6168d26 (diff) | |
| download | linux-941baf6febaa88c057192084ca280d976c7c7239.tar.bz2 | |
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>
Diffstat (limited to 'include/linux/init.h')
| -rw-r--r-- | include/linux/init.h | 1 |
1 files changed, 1 insertions, 0 deletions
diff --git a/include/linux/init.h b/include/linux/init.h index 077d7f93b402..2e96756fe1ff 100644 --- a/include/linux/init.h +++ b/include/linux/init.h @@ -143,6 +143,7 @@ struct file_system_type; extern int do_one_initcall(initcall_t fn); extern char __initdata boot_command_line[]; extern char *saved_command_line; +extern unsigned int saved_command_line_len; extern unsigned int reset_devices; /* used by init/main.c */ |