Hello mailing list! I've read some code in the NFS4.1 client. I have trouble to access variables in a list_head. So I have : (include/linux/sunrpc/xprt.h line 168) struct rpc_xprt{ . . struct rpc_wait_queue pending; /* requests in flight */ . . } ==> struct rpc_wait_queue { . struct list_head tasks[RPC_NR_PRIORITY]; /* task queue for each priority level */ . } The struct "list_head" is a classical linked list. But How do I know the type of the struct in this list? I can maybe guess the struct in it : struct rpc_task {} But how can I be certain that "struct list_head tasks" contains some "struct rpc_task"? I'm new here, thank you for your help! Martin
On Fri, Jun 17, 2016 at 3:41 PM, Martin Houry <martinhoury@gmail.com> wrote:
Hello mailing list! I've read some code in the NFS4.1 client. I have trouble to access variables in a list_head.
So I have : (include/linux/sunrpc/xprt.h line 168) struct rpc_xprt{ . .
struct rpc_wait_queue pending; /* requests in flight */ . . }
==>
struct rpc_wait_queue { . struct list_head tasks[RPC_NR_PRIORITY]; /* task queue for each priority level */ . }
The struct "list_head" is a classical linked list. But How do I know the type of the struct in this list? I can maybe guess the struct in it :
struct rpc_task {}
But how can I be certain that "struct list_head tasks" contains some "struct rpc_task"?
some magic value perhaps?
I'm new here, thank you for your help! Martin
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Bogdan PRICOP ---------------------------------------- Mobile: +353 86 075 3349 E-mail: pricopb@gmail.com ---------------------------------------- On 17 June 2016 at 11:35, Pranay Srivastava <pranjas@gmail.com> wrote:
On Fri, Jun 17, 2016 at 3:41 PM, Martin Houry <martinhoury@gmail.com> wrote:
Hello mailing list! I've read some code in the NFS4.1 client. I have trouble to access variables in a list_head.
So I have : (include/linux/sunrpc/xprt.h line 168) struct rpc_xprt{ . .
struct rpc_wait_queue pending; /* requests in flight */ . . }
==>
struct rpc_wait_queue { . struct list_head tasks[RPC_NR_PRIORITY]; /* task queue for each priority level */ . }
The struct "list_head" is a classical linked list. But How do I know the type of the struct in this list? I can maybe guess the struct in it :
struct rpc_task {}
But how can I be certain that "struct list_head tasks" contains some "struct rpc_task"?
some magic value perhaps?
I'm new here, thank you for your help! Martin
Hi Martin, I think the main idea behind Linux kernel implementation of the linked list (struct list_head) is to work with any kind of items which need to be linked. Please have a look at the below links which explain the internals of Linux kernel list and its usage: https://isis.poly.edu/kulesh/stuff/src/klist/ http://www.makelinux.net/ldd3/chp-11-sect-5 Thanks, Bogdan
On Mon, 20 Jun 2016, Bogdan PRICOP wrote:
Bogdan PRICOP ---------------------------------------- Mobile: +353 86 075 3349 E-mail: pricopb@gmail.com ----------------------------------------
On 17 June 2016 at 11:35, Pranay Srivastava <pranjas@gmail.com> wrote:
On Fri, Jun 17, 2016 at 3:41 PM, Martin Houry <martinhoury@gmail.com> wrote:
Hello mailing list! I've read some code in the NFS4.1 client. I have trouble to access variables in a list_head.
So I have : (include/linux/sunrpc/xprt.h line 168) struct rpc_xprt{ . .
struct rpc_wait_queue pending; /* requests in flight */ . . }
==>
struct rpc_wait_queue { . struct list_head tasks[RPC_NR_PRIORITY]; /* task queue for each priority level */ . }
The struct "list_head" is a classical linked list. But How do I know the type of the struct in this list? I can maybe guess the struct in it :
struct rpc_task {}
But how can I be certain that "struct list_head tasks" contains some "struct rpc_task"?
some magic value perhaps?
I'm new here, thank you for your help! Martin
Hi Martin,
I think the main idea behind Linux kernel implementation of the linked list (struct list_head) is to work with any kind of items which need to be linked.
Please have a look at the below links which explain the internals of Linux kernel list and its usage: https://isis.poly.edu/kulesh/stuff/src/klist/ http://www.makelinux.net/ldd3/chp-11-sect-5
i wrote a page on that way back here: http://crashcourse.ca/introduction-linux-kernel-programming/intermission-let... as part of a kernel programming course that i *really* need to get back to someday and update. *sigh*. rday -- ======================================================================== Robert P. J. Day Ottawa, Ontario, CANADA http://crashcourse.ca Twitter: http://twitter.com/rpjday LinkedIn: http://ca.linkedin.com/in/rpjday ========================================================================
participants (4)
-
Bogdan PRICOP -
Martin Houry -
Pranay Srivastava -
Robert P. J. Day