Messages in this thread Patch in this message | | | Date | Mon, 7 Jul 2003 16:26:21 -0700 (PDT) | From | Davide Libenzi <> | Subject | Re: epoll vs stdin/stdout |
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On Mon, 7 Jul 2003, Davide Libenzi wrote:
> On Mon, 7 Jul 2003, Eric Varsanyi wrote: > > > On Mon, Jul 07, 2003 at 11:57:02AM -0700, Davide Libenzi wrote: > > > Events caught by epoll comes from a file* since that is the abstraction > > > the kernel handles. Events really happen on the file* and there's no way > > > if you dup()ing 1000 times a single fd, to say that events are for fd = 122. > > > > It is useful/mildly common at the app level to want to get read events > > for fd0 and write avail events for fd1. An app that might want to deal > > with reads from stdin in one process and writes to stdout in another > > (something like "team" perhaps) would have trouble here too. > > > > Epoll's API/impl is great as it is IMO, not suggesting need for change, I was > > hoping there was a good standard trick someone worked up to get around > > this specifc end case of stdin/stdout usually being dups but sometimes > > not. Porting my event system over to use epoll was easy/straightforward > > except for this one minor hitch. > > > > I considered: > > - using a second epoll object just for one of the fd's (to inspire > > delivery of the event to 2 wait queues in the kernel); a little > > ugly because of need to stack another epfd under the main one > > just for stdout write events > > > > - select() on (0, 1, epfd) and just use epoll with a timeout of 0 > > when select fires to gather bulk of events; morally similar to > > previous but using select (which I want to just get away from) > > > > - make the app use stdin as its output (this is what I ended up doing); > > breaks redirection of stdout but that doesn't matter to this app > > Any of the above. Pls wait for an incoming patch ...
Try out this one, either over 2.5.74 or over an existing epoll-patched 2.4.{20,21} ...
- Davide
diff -Nru linux-2.5.74.vanilla/fs/eventpoll.c linux-2.5.74.epoll/fs/eventpoll.c --- linux-2.5.74.vanilla/fs/eventpoll.c 2003-07-07 15:22:37.000000000 -0700 +++ linux-2.5.74.epoll/fs/eventpoll.c 2003-07-07 15:40:44.000000000 -0700 @@ -245,6 +245,9 @@ /* The "container" of this item */ struct eventpoll *ep;
+ /* The file descriptor this item refers to */ + int fd; + /* The file this item refers to */ struct file *file;
@@ -285,15 +288,17 @@ static int ep_alloc_pages(char **pages, int numpages); static int ep_free_pages(char **pages, int numpages); static int ep_file_init(struct file *file, unsigned int hashbits); -static unsigned int ep_hash_index(struct eventpoll *ep, struct file *file); +static unsigned int ep_hash_index(struct eventpoll *ep, struct file *file, int fd); static struct list_head *ep_hash_entry(struct eventpoll *ep, unsigned int index); static int ep_init(struct eventpoll *ep, unsigned int hashbits); static void ep_free(struct eventpoll *ep); -static struct epitem *ep_find(struct eventpoll *ep, struct file *file); +static struct epitem *ep_find(struct eventpoll *ep, struct file *file, int fd); static void ep_use_epitem(struct epitem *epi); static void ep_release_epitem(struct epitem *epi); -static void ep_ptable_queue_proc(struct file *file, wait_queue_head_t *whead, poll_table *pt); -static int ep_insert(struct eventpoll *ep, struct epoll_event *event, struct file *tfile); +static void ep_ptable_queue_proc(struct file *file, wait_queue_head_t *whead, + poll_table *pt); +static int ep_insert(struct eventpoll *ep, struct epoll_event *event, + struct file *tfile, int fd); static int ep_modify(struct eventpoll *ep, struct epitem *epi, struct epoll_event *event); static void ep_unregister_pollwait(struct eventpoll *ep, struct epitem *epi); static int ep_unlink(struct eventpoll *ep, struct epitem *epi); @@ -580,7 +585,7 @@ down_write(&ep->sem);
/* Try to lookup the file inside our hash table */ - epi = ep_find(ep, tfile); + epi = ep_find(ep, tfile, fd);
error = -EINVAL; switch (op) { @@ -588,7 +593,7 @@ if (!epi) { epds.events |= POLLERR | POLLHUP;
- error = ep_insert(ep, &epds, tfile); + error = ep_insert(ep, &epds, tfile, fd); } else error = -EEXIST; break; @@ -814,10 +819,11 @@ /* * Calculate the index of the hash relative to "file". */ -static unsigned int ep_hash_index(struct eventpoll *ep, struct file *file) +static unsigned int ep_hash_index(struct eventpoll *ep, struct file *file, int fd) { + unsigned long ptr = (unsigned long) file ^ (fd << ep->hashbits);
- return (unsigned int) hash_ptr(file, ep->hashbits); + return (unsigned int) hash_ptr((void *) ptr, ep->hashbits); }
@@ -920,7 +926,7 @@ * the returned item, so the caller must call ep_release_epitem() * after finished using the "struct epitem". */ -static struct epitem *ep_find(struct eventpoll *ep, struct file *file) +static struct epitem *ep_find(struct eventpoll *ep, struct file *file, int fd) { unsigned long flags; struct list_head *lsthead, *lnk; @@ -928,11 +934,11 @@
read_lock_irqsave(&ep->lock, flags);
- lsthead = ep_hash_entry(ep, ep_hash_index(ep, file)); + lsthead = ep_hash_entry(ep, ep_hash_index(ep, file, fd)); list_for_each(lnk, lsthead) { epi = list_entry(lnk, struct epitem, llink);
- if (epi->file == file) { + if (epi->file == file && epi->fd == fd) { ep_use_epitem(epi); break; } @@ -976,7 +982,8 @@ * This is the callback that is used to add our wait queue to the * target file wakeup lists. */ -static void ep_ptable_queue_proc(struct file *file, wait_queue_head_t *whead, poll_table *pt) +static void ep_ptable_queue_proc(struct file *file, wait_queue_head_t *whead, + poll_table *pt) { struct epitem *epi = EP_ITEM_FROM_EPQUEUE(pt); struct eppoll_entry *pwq; @@ -995,7 +1002,8 @@ }
-static int ep_insert(struct eventpoll *ep, struct epoll_event *event, struct file *tfile) +static int ep_insert(struct eventpoll *ep, struct epoll_event *event, + struct file *tfile, int fd) { int error, revents, pwake = 0; unsigned long flags; @@ -1014,6 +1022,7 @@ INIT_LIST_HEAD(&epi->pwqlist); epi->ep = ep; epi->file = tfile; + epi->fd = fd; epi->event = *event; atomic_set(&epi->usecnt, 1); epi->nwait = 0; @@ -1046,7 +1055,7 @@ write_lock_irqsave(&ep->lock, flags);
/* Add the current item to the hash table */ - list_add(&epi->llink, ep_hash_entry(ep, ep_hash_index(ep, tfile))); + list_add(&epi->llink, ep_hash_entry(ep, ep_hash_index(ep, tfile, fd)));
/* If the file is already "ready" we drop it inside the ready list */ if ((revents & event->events) && !EP_IS_LINKED(&epi->rdllink)) { @@ -1065,8 +1074,8 @@ if (pwake) ep_poll_safewake(&psw, &ep->poll_wait);
- DNPRINTK(3, (KERN_INFO "[%p] eventpoll: ep_insert(%p, %p)\n", - current, ep, tfile)); + DNPRINTK(3, (KERN_INFO "[%p] eventpoll: ep_insert(%p, %p, %d)\n", + current, ep, tfile, fd));
return 0;
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