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Disadvantages of strlen() in Embedded Domain

· One min read

To read from a "TCP Communication" you are probably using read. The prototype for read is

ssize_t read(int fildes, void *buf, size_t nbyte);

and the return value is the number of bytes read (even if they are 0). So, let's say you're about to read 10 bytes, all of which are 0. You have an array with more than enough to hold all the data

int fildes;
char data[1000];
// fildes = TCPConnection
nbytes = read(fildes, data, 1000);

Now, by inspecting nbytes you know you have read 10 bytes. If you check data[0] through data[9] you will find they have 0;

Reference​

Useful Macro that can be a template

· One min read
#define SYSCALL_DEFINE(name) static inline long SYSC_##name
#define SYSCALL_DEFINE0(name)    asmlinkage long sys_##name(void)
#define SYSCALL_DEFINE1(name, ...) SYSCALL_DEFINEx(1, _##name, __VA_ARGS__)
#define SYSCALL_DEFINE2(name, ...) SYSCALL_DEFINEx(2, _##name, __VA_ARGS__)
#define SYSCALL_DEFINE3(name, ...) SYSCALL_DEFINEx(3, _##name, __VA_ARGS__)
#define SYSCALL_DEFINE4(name, ...) SYSCALL_DEFINEx(4, _##name, __VA_ARGS__)
#define SYSCALL_DEFINE5(name, ...) SYSCALL_DEFINEx(5, _##name, __VA_ARGS__)
#define SYSCALL_DEFINE6(name, ...) SYSCALL_DEFINEx(6, _##name, __VA_ARGS__)


/*
 * Example
 */

/**
 * sys_sched_setparam - set/change the RT priority of a thread
 * @pid: the pid in question.
 * @param: structure containing the new RT priority.
 */
SYSCALL_DEFINE2(sched_setparam, pid_t, pid, struct sched_param __user *, param)
{
 return do_sched_setscheduler(pid, -1, param);
}

#define SYSCALL_DEFINE(name) static inline long SYSC_##name
#define SYSCALL_DEFINE0(name)    asmlinkage long sys_##name(void)
#define SYSCALL_DEFINE1(name, ...) SYSCALL_DEFINEx(1, _##name, __VA_ARGS__)
#define SYSCALL_DEFINE2(name, ...) SYSCALL_DEFINEx(2, _##name, __VA_ARGS__)
#define SYSCALL_DEFINE3(name, ...) SYSCALL_DEFINEx(3, _##name, __VA_ARGS__)
#define SYSCALL_DEFINE4(name, ...) SYSCALL_DEFINEx(4, _##name, __VA_ARGS__)
#define SYSCALL_DEFINE5(name, ...) SYSCALL_DEFINEx(5, _##name, __VA_ARGS__)
#define SYSCALL_DEFINE6(name, ...) SYSCALL_DEFINEx(6, _##name, __VA_ARGS__)


/*
 * Example
 */

/**
 * sys_sched_setparam - set/change the RT priority of a thread
 * @pid: the pid in question.
 * @param: structure containing the new RT priority.
 */
SYSCALL_DEFINE2(sched_setparam, pid_t, pid, struct sched_param __user *, param)
{
 return do_sched_setscheduler(pid, -1, param);
}