[musl] [PATCH v2 0/8] use new SYS_fchmodat2 syscall to implement fchmodat with flags

["Gaël PORTAY" <gael.portay@rtone.fr>]

hello,

this patch serie adds the syscall SYS_fchmodat2 to implement fchmodat().
it has landed in linux v6.6.

fhe first five patches catch up the gap of syscall numbers.

the sixth patch removes the spurious flag argument from the syscall
SYS_fchmodat (linux lacks for that argument actually).

the seventh patch defines the syscall itself in headers.

the last patch uses the syscall SYS_fchmodat2 to implement fchmodat() if
flags are passed. the same way the syscall SYS_faccessat2 was used to
implement faccessat() with flags.

it wat tested locally on x86_64 (only), with a dummy test-fchmodat.c.

here is what strace says if no flags are passed:

	gportay@archlinux ~/src/musl $ strace ./lib/libc.so ./test-fchmodat . file 0664 0
	execve("./lib/libc.so", ["./lib/libc.so", "./test-fchmodat", ".", "file", "0664", "0"], 0x7ffc172ccc68 /* 34 vars */) = 0
	arch_prctl(ARCH_SET_FS, 0x765732cf7ba8) = 0
	set_tid_address(0x765732cf8018)         = 367709
	open("./test-fchmodat", O_RDONLY|O_LARGEFILE) = 3
	read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\260\20\0\0\0\0\0\0"..., 960) = 960
	mmap(NULL, 20480, PROT_READ, MAP_PRIVATE, 3, 0) = 0x765732c58000
	mmap(0x765732c59000, 4096, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_FIXED, 3, 0x1000) = 0x765732c59000
	mmap(0x765732c5a000, 4096, PROT_READ, MAP_PRIVATE|MAP_FIXED, 3, 0x2000) = 0x765732c5a000
	mmap(0x765732c5b000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED, 3, 0x2000) = 0x765732c5b000
	close(3)                                = 0
	brk(NULL)                               = 0x5555568a6000
	brk(0x5555568a8000)                     = 0x5555568a8000
	mmap(0x5555568a6000, 4096, PROT_NONE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x5555568a6000
	mprotect(0x765732cf4000, 4096, PROT_READ) = 0
	mprotect(0x765732c5b000, 4096, PROT_READ) = 0
	fchmodat(AT_FDCWD, "file", 0664)        = 0
	exit_group(0)                           = ?
	+++ exited with 0 +++

it uses the syscall fchmodat.

and what strace says if AT_SYMLINK_NOFOLLOW is passed:

	gportay@archlinux ~/src/musl $ strace ./lib/libc.so ./test-fchmodat . file 0664 0x100
	execve("./lib/libc.so", ["./lib/libc.so", "./test-fchmodat", ".", "file", "0664", "0x100"], 0x7ffcd7228278 /* 34 vars */) = 0
	arch_prctl(ARCH_SET_FS, 0x7318d8907ba8) = 0
	set_tid_address(0x7318d8908018)         = 367715
	open("./test-fchmodat", O_RDONLY|O_LARGEFILE) = 3
	read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\260\20\0\0\0\0\0\0"..., 960) = 960
	mmap(NULL, 20480, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7318d8868000
	mmap(0x7318d8869000, 4096, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_FIXED, 3, 0x1000) = 0x7318d8869000
	mmap(0x7318d886a000, 4096, PROT_READ, MAP_PRIVATE|MAP_FIXED, 3, 0x2000) = 0x7318d886a000
	mmap(0x7318d886b000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED, 3, 0x2000) = 0x7318d886b000
	close(3)                                = 0
	brk(NULL)                               = 0x55555563d000
	brk(0x55555563f000)                     = 0x55555563f000
	mmap(0x55555563d000, 4096, PROT_NONE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x55555563d000
	mprotect(0x7318d8904000, 4096, PROT_READ) = 0
	mprotect(0x7318d886b000, 4096, PROT_READ) = 0
	fchmodat2(AT_FDCWD, "file", 0664, AT_SYMLINK_NOFOLLOW) = 0
	exit_group(0)                           = ?
	+++ exited with 0 +++

it uses the syscall fchmodat2!

	#include <unistd.h>
	#include <stdlib.h>
	#include <stdio.h>
	#include <errno.h>
	#include <string.h>
	
	#include <fcntl.h>
	#include <sys/stat.h>
	
	int main(int argc, char * const argv[])
	{
		int dfd = AT_FDCWD, flags = 0, ret = EXIT_FAILURE;
		mode_t mode;
	
		if (argc < 4) {
			fprintf(stderr, "Too few arguments\n");
			exit(EXIT_FAILURE);
		} else if (argc > 5) {
			fprintf(stderr, "Too many arguments\n");
			exit(EXIT_FAILURE);
		}
	
		mode = strtoul(argv[3], NULL, 0);
		if (argc == 5)
			flags = strtoul(argv[4], NULL, 0);
	
		if (strcmp(argv[1], "-") == 0) {
			dfd = open(argv[1], O_DIRECTORY);
			if (dfd == -1) {
				perror("open");
				return EXIT_FAILURE;
			}
		}
	
		if (fchmodat(dfd, argv[2], mode, flags)) {
			perror("fchmodat");
			goto exit;
		}
	
		ret = EXIT_SUCCESS;
	
	exit:
		if (dfd != AT_FDCWD)
			if (close(dfd))
				perror("close");
	
		return ret;
	}

changes since v1:
 - catchup syscall gap
 - add missing syscall number for aarch64

regards,
Gaël PORTAY (8):
  bits/syscall.h: add process_madvise from linux v5.14
  bits/syscall.h: add process_mrelease from linux v5.15
  bits/syscall.h: add futex_waitv from linux v5.16
  bits/syscall.h: add set_mempolicy_home_node from linux v5.17
  bits/syscall.h: add cachestat from linux v6.4
  remove flag argument from fchmodat syscall
  bits/syscall.h: add __NR_fchmodat2 from linux v6.6
  use new SYS_fchmodat2 syscall to implement fchmodat with flags

 arch/aarch64/bits/syscall.h.in    | 6 ++++++
 arch/arm/bits/syscall.h.in        | 6 ++++++
 arch/i386/bits/syscall.h.in       | 6 ++++++
 arch/m68k/bits/syscall.h.in       | 6 ++++++
 arch/microblaze/bits/syscall.h.in | 6 ++++++
 arch/mips/bits/syscall.h.in       | 6 ++++++
 arch/mips64/bits/syscall.h.in     | 6 ++++++
 arch/mipsn32/bits/syscall.h.in    | 6 ++++++
 arch/or1k/bits/syscall.h.in       | 6 ++++++
 arch/powerpc/bits/syscall.h.in    | 6 ++++++
 arch/powerpc64/bits/syscall.h.in  | 6 ++++++
 arch/riscv64/bits/syscall.h.in    | 6 ++++++
 arch/s390x/bits/syscall.h.in      | 6 ++++++
 arch/sh/bits/syscall.h.in         | 6 ++++++
 arch/x32/bits/syscall.h.in        | 6 ++++++
 arch/x86_64/bits/syscall.h.in     | 6 ++++++
 src/stat/fchmodat.c               | 7 ++++++-
 17 files changed, 102 insertions(+), 1 deletion(-)

-- 
2.43.2