a signal is sent to a process, either from the kernel or from another
process, the kernel generates it by invoking the
force_sig( ), or
force_sig_info( ) functions. These accomplish the first phase of signal
handling described earlier in Section 10.1, updating the process
descriptor as needed. They do not directly perform the second phase
of delivering the signal but, depending on the type of signal and the
state of the process, may wake up the process and force it to receive
send_sig_info( ) function acts on three parameters:
The signal number.
Either the address of a
siginfo_t table or one of
two special values. 0 means that the signal has been sent by a User
Mode process, while 1 means that it has been sent by the kernel.
A pointer to the descriptor of the destination process.
send_sig_info( ) function starts by checking
whether the parameters are correct:
if (sig < 0 || sig > 64) return -EINVAL;
The function then checks if the signal is being sent by a User Mode
process. This occurs when
info is equal to 0 or
si_code field of the
siginfo_t table is negative or 0 (positive values
of this field mean that the signal was sent by some kernel function):
if ((!info || ((unsigned long)info != 1 && (info->si_code <=0))) && ((sig != SIGCONT) || (current->session != t->session)) && (current->euid ^ t->suid) && (current->euid ^ t->uid) && (current->uid ...