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Top Forums UNIX for Dummies Questions & Answers a for loop that doesn't make sense Post 302240964 by sdsd on Saturday 27th of September 2008 07:35:28 AM
Old 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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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)
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