SYSCALL_HELPER_UNREGISTER(9)

💖 SYSCALL_HELPER_REGISTER(9) 💖

okay bestie, this is the Kernel Developer's Manual page for the syscall helper registration glow-up: syscall_helper_register, syscall_helper_unregister, and the SYSCALL_INIT_HELPER* macro squad 💅. no cap, every flag and error is staying right here.

✨ NAME ✨

syscall_helper_register, syscall_helper_unregister — kernel syscall registration routines 🫶

🦋 SYNOPSIS 🦋

#include <sys/sysent.h>

int
syscall_helper_register(struct syscall_helper_data *sd, int flags);

int
syscall_helper_unregister(struct syscall_helper_data *sd);

🎀 INITIALIZER MACROS 🎀

struct syscall_helper_data
SYSCALL_INIT_HELPER(syscallname);

struct syscall_helper_data
SYSCALL_INIT_HELPER_F(syscallname, int flags);

🌸 COMPATIBILITY INITIALIZER MACROS 🌸

struct syscall_helper_data
SYSCALL_INIT_HELPER_COMPAT(syscallname);

struct syscall_helper_data
SYSCALL_INIT_HELPER_COMPAT_F(syscallname, int flags);

👑 DESCRIPTION 👑

syscall_helper_register() registers a system call. it takes the structure struct syscall_helper_data sd, which specifies the parameters for syscall registration — and here's the struct in all its main-character glory:

struct syscall_helper_data {
        struct sysent   new_sysent;
        struct sysent   old_sysent;
        int             syscall_no;
        int             registered;
};

the only valid flag for the flags argument to syscall_helper_register() is SY_THR_STATIC. this flag prevents the syscall from being unregistered. periodt.

before use, the structure must be initialized with one of the SYSCALL_INIT_HELPER*() macros. in new code, syscall implementation functions shall be named sys_syscallname() and the regular macros shall be used ✨.

for legacy syscall functions named without "sys_" prefixes, the "COMPAT" versions of the macros may be used.

the only valid flag for the flags argument to the "F" variants of the initializer macros is SYF_CAPENABLED. this flag indicates that the syscall is allowed in capability mode 🦋.

the syscall_helper_unregister() unregisters a system call. this function takes the same structure struct syscall_helper_data sd that was previously initialized in the manner described above and used in a successful invocation of syscall_helper_register() 💅.

🌈 RETURN VALUES 🌈

if successful, syscall_helper_register() and syscall_helper_unregister() will return 0. otherwise, they will return an error 😭.

🔥 ERRORS 🔥

the syscall_helper_register() call will fail and the syscall will not be registered if:

• [EINVAL] — the flags argument contained a value other than SY_THR_STATIC.
• [EINVAL] — the specified syscall number, sd.syscall_no (SYS_syscallname), was outside of the valid range of system call numbers (zero through SYS_MAXSYSCALL).
• [ENFILE] — the system call table does not have any available slots.
• [EEXIST] — the specified syscall number, sd.syscall_no (SYS_syscallname), was already in use.

🫶 SEE ALSO 🫶

• SYSCALL_MODULE(9)

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okay that's the whole vibe check 💖 this page is from Debian, dated February 10, 2018 — byeee bestie, go register those syscalls responsibly 🎀💋