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Commit 252e5725 authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Linus Torvalds
Browse files

do_sys_poll: simplify playing with on-stack data 



Cleanup. Lessens both the source and compiled code (100 bytes) and imho makes
the code much more understandable.

With this patch "struct poll_list *head" always points to on-stack stack_pps,
so we can remove all "is it on-stack" and "was it initialized" checks.

Also, move poll_initwait/poll_freewait and -EINTR detection closer to the
do_poll()'s callsite.

[akpm@linux-foundation.org: fix warning (size_t != uint)]
Signed-off-by: default avatarOleg Nesterov <oleg@tv-sign.ru>
Looks-good-to: Andi Kleen <ak@suse.de>
Cc: Davide Libenzi <davidel@xmailserver.org>
Cc: Vadim Lobanov <vlobanov@speakeasy.net>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 759d7c6c

fs/select.c

+36 −56
Original line number Diff line number Diff line
@@ -651,86 +651,66 @@ static int do_poll(unsigned int nfds, struct poll_list *list, 
int do_sys_poll(struct pollfd __user *ufds, unsigned int nfds, s64 *timeout)

{

	struct poll_wqueues table;

 	int fdcount, err;

 	unsigned int i;

	struct poll_list *head;

 	struct poll_list *walk;

 	int err = -EFAULT, fdcount, len, size;

	/* Allocate small arguments on the stack to save memory and be

	   faster - use long to make sure the buffer is aligned properly

	   on 64 bit archs to avoid unaligned access */

	long stack_pps[POLL_STACK_ALLOC/sizeof(long)];

	struct poll_list *stack_pp = NULL;

	struct poll_list *const head = (struct poll_list *)stack_pps;

 	struct poll_list *walk = head;

 	unsigned long todo = nfds;



	/* Do a sanity check on nfds ... */

	if (nfds > current->signal->rlim[RLIMIT_NOFILE].rlim_cur)

		return -EINVAL;



	poll_initwait(&table);

	len = min_t(unsigned int, nfds, N_STACK_PPS);

	for (;;) {

		walk->next = NULL;

		walk->len = len;

		if (!len)

			break;



	head = NULL;

	walk = NULL;

	i = nfds;

	err = -ENOMEM;

	while(i!=0) {

		struct poll_list *pp;

		int num, size;

		if (stack_pp == NULL)

			num = N_STACK_PPS;

		else

			num = POLLFD_PER_PAGE;

		if (num > i)

			num = i;

		size = sizeof(struct poll_list) + sizeof(struct pollfd)*num;

		if (!stack_pp)

			stack_pp = pp = (struct poll_list *)stack_pps;

		else {

			pp = kmalloc(size, GFP_KERNEL);

			if (!pp)

		if (copy_from_user(walk->entries, ufds + nfds-todo,

					sizeof(struct pollfd) * walk->len))

			goto out_fds;

		}

		pp->next=NULL;

		pp->len = num;

		if (head == NULL)

			head = pp;

		else

			walk->next = pp;



		walk = pp;

		if (copy_from_user(pp->entries, ufds + nfds-i, 

				sizeof(struct pollfd)*num)) {

			err = -EFAULT;

		todo -= walk->len;

		if (!todo)

			break;



		len = min(todo, POLLFD_PER_PAGE);

		size = sizeof(struct poll_list) + sizeof(struct pollfd) * len;

		walk = walk->next = kmalloc(size, GFP_KERNEL);

		if (!walk) {

			err = -ENOMEM;

			goto out_fds;

		}

		i -= pp->len;

	}



	poll_initwait(&table);

	fdcount = do_poll(nfds, head, &table, timeout);

	if (!fdcount && signal_pending(current))

		fdcount = -EINTR;

	poll_freewait(&table);



	/* OK, now copy the revents fields back to user space. */

	walk = head;

	err = -EFAULT;

	while(walk != NULL) {

	for (walk = head; walk; walk = walk->next) {

		struct pollfd *fds = walk->entries;

		int j;



		for (j=0; j < walk->len; j++, ufds++) {

		for (j = 0; j < walk->len; j++, ufds++)

			if (__put_user(fds[j].revents, &ufds->revents))

				goto out_fds;

  	}

		walk = walk->next;

  	}



	err = fdcount;

	if (!fdcount && signal_pending(current))

		err = -EINTR;

out_fds:

	walk = head;

	while(walk!=NULL) {

		struct poll_list *pp = walk->next;

		if (walk != stack_pp)

			kfree(walk);

		walk = pp;

	walk = head->next;

	while (walk) {

		struct poll_list *pos = walk;

		walk = walk->next;

		kfree(pos);

	}

	poll_freewait(&table);



	return err;

}