09-27-2008
a for loop that doesn't make sense
I've been referring bash info for processes and came across a structure for a process which is defined like
typedef struct process
{
struct process *next;
char ** argv
.
.
.
}process;
What I don't understand is that in the program there's a for loop which goes like this
job *j;//pointer to a structure that holds data about the jobs running
process *p;//pointer to a structure that holds process information
for(p=j->first_process;p;p=p->next) {...}
I don't understand how the p highlighted in red can be used as a condition in a for loop. What purpose does it serve? How does the for loop evaluate p as a terminating condition for the loop?
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LEARN ABOUT CENTOS
call_usermodehelper_setup
CALL_USERMODEHELPER_(9) Module Support CALL_USERMODEHELPER_(9)
NAME
call_usermodehelper_setup - prepare to call a usermode helper
SYNOPSIS
struct subprocess_info * call_usermodehelper_setup(char * path, char ** argv, char ** envp, gfp_t gfp_mask,
int (*init) (struct subprocess_info *info, struct cred *new),
void (*cleanup) (struct subprocess_info *info), void * data);
ARGUMENTS
path
path to usermode executable
argv
arg vector for process
envp
environment for process
gfp_mask
gfp mask for memory allocation
init
an init function
cleanup
a cleanup function
data
arbitrary context sensitive data
DESCRIPTION
Returns either NULL on allocation failure, or a subprocess_info structure. This should be passed to call_usermodehelper_exec to exec the
process and free the structure.
The init function is used to customize the helper process prior to exec. A non-zero return code causes the process to error out, exit, and
return the failure to the calling process
The cleanup function is just before ethe subprocess_info is about to be freed. This can be used for freeing the argv and envp. The Function
must be runnable in either a process context or the context in which call_usermodehelper_exec is called.
COPYRIGHT
Kernel Hackers Manual 3.10 June 2014 CALL_USERMODEHELPER_(9)