Re: [PATCH] eventfd: implementation of EFD_MASK flag
On 2015-08-11 6:16 AM, Martin Sustrik wrote: On 2015-08-10 10:57, Damian Hobson-Garcia wrote: Hi Martin, Thanks for your comments. On 2015-08-10 3:39 PM, Martin Sustrik wrote: On 2015-08-10 08:23, Damian Hobson-Garcia wrote: Replying to my own post, but I had the following comments/questions. Martin, if you have any response to my comments I would be very happy to hear them. On 2015-08-10 2:51 PM, Damian Hobson-Garcia wrote: From: Martin Sustrik sust...@250bpm.com [snip] write(2): User is allowed to write only buffers containing the following structure: struct efd_mask { __u32 events; __u64 data; }; The value of 'events' should be any combination of event flags as defined by poll(2) function (POLLIN, POLLOUT, POLLERR, POLLHUP etc.) Specified events will be signaled when polling (select, poll, epoll) on the eventfd is done later on. 'data' is opaque data that are not interpreted by eventfd object. I'm not fully clear on the purpose that the 'data' member serves. Does this opaque handle need to be tied together with this event synchronization construct? It's a convenience thing. Imagine you are implementing your own file descriptor type in user space. You create an EFD_MASK socket and a structure that will hold any state that you need for the socket (tx/rx buffers and such). Now you have two things to pass around. If you want to pass the fd to a function, it must have two parameters (fd and pointer to the structure). To fix it you can put the fd into the structure. That way there's only one thing to pass around (the structure). The problem with that approach is when you have generic code that deals with file descriptors. For example, a simple poller which accepts a list of (fd, callback) pairs and invokes the callback when one of the fds signals POLLIN. You can't send a pointer to a structure to such function. All you can send is the fd, but then, when the callback is invoked, fd is all you have. You have no idea where your state is. 'data' member allows you to put the pointer to the state to the socket itself. Thus, if you have a fd, you can always find out where the associated data is by reading the mask structure from the fd. Ok, I see what you're saying. I guess that keeping track of the mapping between the fd and the struct in user space could be non-trivial if there are a large number of active fds that are polling very frequently. Wouldn't it be sufficient to just use epoll() in this case though? It already seems to support this kind of thing. My use case was like this: int s = mysocket(); ... // myrecv() can get the pointer to the structure // without user having to pass it as an argument myrecv(s, buf, sizeof(buf)); However, same behaviour can be accomplished by simply keeping a static array of pointers in the user space. So let's cut this part out of the patch. Ok, I'll drop the 'data' member. I could add some padding to the efd_mask structure so that it is the same size as the 64-bit data size used when EFD_MASK is not set. [snip] @@ -55,6 +69,9 @@ __u64 eventfd_signal(struct eventfd_ctx *ctx, __u64 n) { +/* This function should never be used with eventfd in the mask mode. */ +BUG_ON(ctx-flags EFD_MASK); + ... @@ -158,6 +180,9 @@ int eventfd_ctx_remove_wait_queue(struct eventfd_ctx *ctx, wait_queue_t *wait, { +/* This function should never be used with eventfd in the mask mode. */ +BUG_ON(ctx-flags EFD_MASK); + ... @@ -188,6 +213,9 @@ ssize_t eventfd_ctx_read(struct eventfd_ctx *ctx, int no_wait, __u64 *cnt) +/* This function should never be used with eventfd in the mask mode. */ +BUG_ON(ctx-flags EFD_MASK); + If eventfd_ctx_fileget() returns EINVAL when EFD_MASK is set, I don't think that there will be a way to call these functions in the mask mode, so it should be possible to get rid of the BUG_ON checks. Sure. Feel free to do so. [snip] @@ -230,6 +258,19 @@ static ssize_t eventfd_read(struct file *file, char __user *buf, size_t count, ssize_t res; __u64 cnt; +if (ctx-flags EFD_MASK) { +struct efd_mask mask; + +if (count sizeof(mask)) +return -EINVAL; +spin_lock_irq(ctx-wqh.lock); +mask = ctx-mask; +spin_unlock_irq(ctx-wqh.lock); +if (copy_to_user(buf, mask, sizeof(mask))) +return -EFAULT; +return sizeof(mask); +} + For the other eventfd modes, reading the value will update the internal state of the eventfd (either clearing or decrementing the counter). Should something similar be done here? I'm thinking of a case where a process is polling on this fd in a loop. Clearing the efd_mask data on read should provide an easy way for the polling process to know if it is seeing new poll events. No. In this case reading the value has no effect on the state of the fd. How it should work is rather: // fd is in POLLIN
Re: [PATCH] eventfd: implementation of EFD_MASK flag
On 2015-08-10 10:57, Damian Hobson-Garcia wrote: Hi Martin, Thanks for your comments. On 2015-08-10 3:39 PM, Martin Sustrik wrote: On 2015-08-10 08:23, Damian Hobson-Garcia wrote: Replying to my own post, but I had the following comments/questions. Martin, if you have any response to my comments I would be very happy to hear them. On 2015-08-10 2:51 PM, Damian Hobson-Garcia wrote: From: Martin Sustrik sust...@250bpm.com [snip] write(2): User is allowed to write only buffers containing the following structure: struct efd_mask { __u32 events; __u64 data; }; The value of 'events' should be any combination of event flags as defined by poll(2) function (POLLIN, POLLOUT, POLLERR, POLLHUP etc.) Specified events will be signaled when polling (select, poll, epoll) on the eventfd is done later on. 'data' is opaque data that are not interpreted by eventfd object. I'm not fully clear on the purpose that the 'data' member serves. Does this opaque handle need to be tied together with this event synchronization construct? It's a convenience thing. Imagine you are implementing your own file descriptor type in user space. You create an EFD_MASK socket and a structure that will hold any state that you need for the socket (tx/rx buffers and such). Now you have two things to pass around. If you want to pass the fd to a function, it must have two parameters (fd and pointer to the structure). To fix it you can put the fd into the structure. That way there's only one thing to pass around (the structure). The problem with that approach is when you have generic code that deals with file descriptors. For example, a simple poller which accepts a list of (fd, callback) pairs and invokes the callback when one of the fds signals POLLIN. You can't send a pointer to a structure to such function. All you can send is the fd, but then, when the callback is invoked, fd is all you have. You have no idea where your state is. 'data' member allows you to put the pointer to the state to the socket itself. Thus, if you have a fd, you can always find out where the associated data is by reading the mask structure from the fd. Ok, I see what you're saying. I guess that keeping track of the mapping between the fd and the struct in user space could be non-trivial if there are a large number of active fds that are polling very frequently. Wouldn't it be sufficient to just use epoll() in this case though? It already seems to support this kind of thing. My use case was like this: int s = mysocket(); ... // myrecv() can get the pointer to the structure // without user having to pass it as an argument myrecv(s, buf, sizeof(buf)); However, same behaviour can be accomplished by simply keeping a static array of pointers in the user space. So let's cut this part out of the patch. [snip] @@ -55,6 +69,9 @@ __u64 eventfd_signal(struct eventfd_ctx *ctx, __u64 n) { +/* This function should never be used with eventfd in the mask mode. */ +BUG_ON(ctx-flags EFD_MASK); + ... @@ -158,6 +180,9 @@ int eventfd_ctx_remove_wait_queue(struct eventfd_ctx *ctx, wait_queue_t *wait, { +/* This function should never be used with eventfd in the mask mode. */ +BUG_ON(ctx-flags EFD_MASK); + ... @@ -188,6 +213,9 @@ ssize_t eventfd_ctx_read(struct eventfd_ctx *ctx, int no_wait, __u64 *cnt) +/* This function should never be used with eventfd in the mask mode. */ +BUG_ON(ctx-flags EFD_MASK); + If eventfd_ctx_fileget() returns EINVAL when EFD_MASK is set, I don't think that there will be a way to call these functions in the mask mode, so it should be possible to get rid of the BUG_ON checks. Sure. Feel free to do so. [snip] @@ -230,6 +258,19 @@ static ssize_t eventfd_read(struct file *file, char __user *buf, size_t count, ssize_t res; __u64 cnt; +if (ctx-flags EFD_MASK) { +struct efd_mask mask; + +if (count sizeof(mask)) +return -EINVAL; +spin_lock_irq(ctx-wqh.lock); +mask = ctx-mask; +spin_unlock_irq(ctx-wqh.lock); +if (copy_to_user(buf, mask, sizeof(mask))) +return -EFAULT; +return sizeof(mask); +} + For the other eventfd modes, reading the value will update the internal state of the eventfd (either clearing or decrementing the counter). Should something similar be done here? I'm thinking of a case where a process is polling on this fd in a loop. Clearing the efd_mask data on read should provide an easy way for the polling process to know if it is seeing new poll events. No. In this case reading the value has no effect on the state of the fd. How it should work is rather: // fd is in POLLIN state poll(fd); // function exits with POLLIN but fd remains in POLLIN state my_recv(fd, buf, size); // my_recv function have found out that there's no more data to recv and switched off the POLLIN flag poll(fd); // we block here waiting for more data to arrive from the network How
Re: [PATCH] eventfd: implementation of EFD_MASK flag
Hi Martin, Thanks for your comments. On 2015-08-10 3:39 PM, Martin Sustrik wrote: On 2015-08-10 08:23, Damian Hobson-Garcia wrote: Replying to my own post, but I had the following comments/questions. Martin, if you have any response to my comments I would be very happy to hear them. On 2015-08-10 2:51 PM, Damian Hobson-Garcia wrote: From: Martin Sustrik sust...@250bpm.com [snip] write(2): User is allowed to write only buffers containing the following structure: struct efd_mask { __u32 events; __u64 data; }; The value of 'events' should be any combination of event flags as defined by poll(2) function (POLLIN, POLLOUT, POLLERR, POLLHUP etc.) Specified events will be signaled when polling (select, poll, epoll) on the eventfd is done later on. 'data' is opaque data that are not interpreted by eventfd object. I'm not fully clear on the purpose that the 'data' member serves. Does this opaque handle need to be tied together with this event synchronization construct? It's a convenience thing. Imagine you are implementing your own file descriptor type in user space. You create an EFD_MASK socket and a structure that will hold any state that you need for the socket (tx/rx buffers and such). Now you have two things to pass around. If you want to pass the fd to a function, it must have two parameters (fd and pointer to the structure). To fix it you can put the fd into the structure. That way there's only one thing to pass around (the structure). The problem with that approach is when you have generic code that deals with file descriptors. For example, a simple poller which accepts a list of (fd, callback) pairs and invokes the callback when one of the fds signals POLLIN. You can't send a pointer to a structure to such function. All you can send is the fd, but then, when the callback is invoked, fd is all you have. You have no idea where your state is. 'data' member allows you to put the pointer to the state to the socket itself. Thus, if you have a fd, you can always find out where the associated data is by reading the mask structure from the fd. Ok, I see what you're saying. I guess that keeping track of the mapping between the fd and the struct in user space could be non-trivial if there are a large number of active fds that are polling very frequently. Wouldn't it be sufficient to just use epoll() in this case though? It already seems to support this kind of thing. [snip] @@ -55,6 +69,9 @@ __u64 eventfd_signal(struct eventfd_ctx *ctx, __u64 n) { +/* This function should never be used with eventfd in the mask mode. */ +BUG_ON(ctx-flags EFD_MASK); + ... @@ -158,6 +180,9 @@ int eventfd_ctx_remove_wait_queue(struct eventfd_ctx *ctx, wait_queue_t *wait, { +/* This function should never be used with eventfd in the mask mode. */ +BUG_ON(ctx-flags EFD_MASK); + ... @@ -188,6 +213,9 @@ ssize_t eventfd_ctx_read(struct eventfd_ctx *ctx, int no_wait, __u64 *cnt) +/* This function should never be used with eventfd in the mask mode. */ +BUG_ON(ctx-flags EFD_MASK); + If eventfd_ctx_fileget() returns EINVAL when EFD_MASK is set, I don't think that there will be a way to call these functions in the mask mode, so it should be possible to get rid of the BUG_ON checks. Sure. Feel free to do so. [snip] @@ -230,6 +258,19 @@ static ssize_t eventfd_read(struct file *file, char __user *buf, size_t count, ssize_t res; __u64 cnt; +if (ctx-flags EFD_MASK) { +struct efd_mask mask; + +if (count sizeof(mask)) +return -EINVAL; +spin_lock_irq(ctx-wqh.lock); +mask = ctx-mask; +spin_unlock_irq(ctx-wqh.lock); +if (copy_to_user(buf, mask, sizeof(mask))) +return -EFAULT; +return sizeof(mask); +} + For the other eventfd modes, reading the value will update the internal state of the eventfd (either clearing or decrementing the counter). Should something similar be done here? I'm thinking of a case where a process is polling on this fd in a loop. Clearing the efd_mask data on read should provide an easy way for the polling process to know if it is seeing new poll events. No. In this case reading the value has no effect on the state of the fd. How it should work is rather: // fd is in POLLIN state poll(fd); // function exits with POLLIN but fd remains in POLLIN state my_recv(fd, buf, size); // my_recv function have found out that there's no more data to recv and switched off the POLLIN flag poll(fd); // we block here waiting for more data to arrive from the network How exactly doe the receiver switch off the POLLIN flag? Does the receiver also write to the eventfd? or do you mean that it just doesn't set POLLIN in the events mask? It seems cleaner to have the sender only write the eventfd and the receiver only read it. Your example would be exactly the same, except that my_recv(fd,
Re: [PATCH] eventfd: implementation of EFD_MASK flag
Replying to my own post, but I had the following comments/questions. Martin, if you have any response to my comments I would be very happy to hear them. On 2015-08-10 2:51 PM, Damian Hobson-Garcia wrote: From: Martin Sustrik sust...@250bpm.com [snip] write(2): User is allowed to write only buffers containing the following structure: struct efd_mask { __u32 events; __u64 data; }; The value of 'events' should be any combination of event flags as defined by poll(2) function (POLLIN, POLLOUT, POLLERR, POLLHUP etc.) Specified events will be signaled when polling (select, poll, epoll) on the eventfd is done later on. 'data' is opaque data that are not interpreted by eventfd object. I'm not fully clear on the purpose that the 'data' member serves. Does this opaque handle need to be tied together with this event synchronization construct? [snip] @@ -55,6 +69,9 @@ __u64 eventfd_signal(struct eventfd_ctx *ctx, __u64 n) { + /* This function should never be used with eventfd in the mask mode. */ + BUG_ON(ctx-flags EFD_MASK); + ... @@ -158,6 +180,9 @@ int eventfd_ctx_remove_wait_queue(struct eventfd_ctx *ctx, wait_queue_t *wait, { + /* This function should never be used with eventfd in the mask mode. */ + BUG_ON(ctx-flags EFD_MASK); + ... @@ -188,6 +213,9 @@ ssize_t eventfd_ctx_read(struct eventfd_ctx *ctx, int no_wait, __u64 *cnt) + /* This function should never be used with eventfd in the mask mode. */ + BUG_ON(ctx-flags EFD_MASK); + If eventfd_ctx_fileget() returns EINVAL when EFD_MASK is set, I don't think that there will be a way to call these functions in the mask mode, so it should be possible to get rid of the BUG_ON checks. [snip] @@ -230,6 +258,19 @@ static ssize_t eventfd_read(struct file *file, char __user *buf, size_t count, ssize_t res; __u64 cnt; + if (ctx-flags EFD_MASK) { + struct efd_mask mask; + + if (count sizeof(mask)) + return -EINVAL; + spin_lock_irq(ctx-wqh.lock); + mask = ctx-mask; + spin_unlock_irq(ctx-wqh.lock); + if (copy_to_user(buf, mask, sizeof(mask))) + return -EFAULT; + return sizeof(mask); + } + For the other eventfd modes, reading the value will update the internal state of the eventfd (either clearing or decrementing the counter). Should something similar be done here? I'm thinking of a case where a process is polling on this fd in a loop. Clearing the efd_mask data on read should provide an easy way for the polling process to know if it is seeing new poll events. @@ -292,8 +351,13 @@ static void eventfd_show_fdinfo(struct seq_file *m, struct file *f) struct eventfd_ctx *ctx = f-private_data; spin_lock_irq(ctx-wqh.lock); - seq_printf(m, eventfd-count: %16llx\n, -(unsigned long long)ctx-count); + if (ctx-flags EFD_MASK) { + seq_printf(m, eventfd-mask: %x\n, + (unsigned)ctx-mask.events); + } else { + seq_printf(m, eventfd-count: %16llx\n, + (unsigned long long)ctx-count); + } spin_unlock_irq(ctx-wqh.lock); } I think that putting the EFD_MASK functionality into a different fops structure might be useful for reducing the number of if statements. Thank you, Damian -- To unsubscribe from this list: send the line unsubscribe netdev in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH] eventfd: implementation of EFD_MASK flag
On 2015-08-10 08:23, Damian Hobson-Garcia wrote: Replying to my own post, but I had the following comments/questions. Martin, if you have any response to my comments I would be very happy to hear them. On 2015-08-10 2:51 PM, Damian Hobson-Garcia wrote: From: Martin Sustrik sust...@250bpm.com [snip] write(2): User is allowed to write only buffers containing the following structure: struct efd_mask { __u32 events; __u64 data; }; The value of 'events' should be any combination of event flags as defined by poll(2) function (POLLIN, POLLOUT, POLLERR, POLLHUP etc.) Specified events will be signaled when polling (select, poll, epoll) on the eventfd is done later on. 'data' is opaque data that are not interpreted by eventfd object. I'm not fully clear on the purpose that the 'data' member serves. Does this opaque handle need to be tied together with this event synchronization construct? It's a convenience thing. Imagine you are implementing your own file descriptor type in user space. You create an EFD_MASK socket and a structure that will hold any state that you need for the socket (tx/rx buffers and such). Now you have two things to pass around. If you want to pass the fd to a function, it must have two parameters (fd and pointer to the structure). To fix it you can put the fd into the structure. That way there's only one thing to pass around (the structure). The problem with that approach is when you have generic code that deals with file descriptors. For example, a simple poller which accepts a list of (fd, callback) pairs and invokes the callback when one of the fds signals POLLIN. You can't send a pointer to a structure to such function. All you can send is the fd, but then, when the callback is invoked, fd is all you have. You have no idea where your state is. 'data' member allows you to put the pointer to the state to the socket itself. Thus, if you have a fd, you can always find out where the associated data is by reading the mask structure from the fd. [snip] @@ -55,6 +69,9 @@ __u64 eventfd_signal(struct eventfd_ctx *ctx, __u64 n) { + /* This function should never be used with eventfd in the mask mode. */ + BUG_ON(ctx-flags EFD_MASK); + ... @@ -158,6 +180,9 @@ int eventfd_ctx_remove_wait_queue(struct eventfd_ctx *ctx, wait_queue_t *wait, { + /* This function should never be used with eventfd in the mask mode. */ + BUG_ON(ctx-flags EFD_MASK); + ... @@ -188,6 +213,9 @@ ssize_t eventfd_ctx_read(struct eventfd_ctx *ctx, int no_wait, __u64 *cnt) + /* This function should never be used with eventfd in the mask mode. */ + BUG_ON(ctx-flags EFD_MASK); + If eventfd_ctx_fileget() returns EINVAL when EFD_MASK is set, I don't think that there will be a way to call these functions in the mask mode, so it should be possible to get rid of the BUG_ON checks. Sure. Feel free to do so. [snip] @@ -230,6 +258,19 @@ static ssize_t eventfd_read(struct file *file, char __user *buf, size_t count, ssize_t res; __u64 cnt; + if (ctx-flags EFD_MASK) { + struct efd_mask mask; + + if (count sizeof(mask)) + return -EINVAL; + spin_lock_irq(ctx-wqh.lock); + mask = ctx-mask; + spin_unlock_irq(ctx-wqh.lock); + if (copy_to_user(buf, mask, sizeof(mask))) + return -EFAULT; + return sizeof(mask); + } + For the other eventfd modes, reading the value will update the internal state of the eventfd (either clearing or decrementing the counter). Should something similar be done here? I'm thinking of a case where a process is polling on this fd in a loop. Clearing the efd_mask data on read should provide an easy way for the polling process to know if it is seeing new poll events. No. In this case reading the value has no effect on the state of the fd. How it should work is rather: // fd is in POLLIN state poll(fd); // function exits with POLLIN but fd remains in POLLIN state my_recv(fd, buf, size); // my_recv function have found out that there's no more data to recv and switched off the POLLIN flag poll(fd); // we block here waiting for more data to arrive from the network @@ -292,8 +351,13 @@ static void eventfd_show_fdinfo(struct seq_file *m, struct file *f) struct eventfd_ctx *ctx = f-private_data; spin_lock_irq(ctx-wqh.lock); - seq_printf(m, eventfd-count: %16llx\n, - (unsigned long long)ctx-count); + if (ctx-flags EFD_MASK) { + seq_printf(m, eventfd-mask: %x\n, +(unsigned)ctx-mask.events); + } else { + seq_printf(m, eventfd-count: %16llx\n, +(unsigned long long)ctx-count); + } spin_unlock_irq(ctx-wqh.lock); } I think that putting the EFD_MASK functionality into a different fops structure might be
[PATCH] eventfd: implementation of EFD_MASK flag
From: Martin Sustrik sust...@250bpm.com When implementing network protocols in user space, one has to implement fake file descriptors to represent the sockets for the protocol. Polling on such fake file descriptors is a problem (poll/select/epoll accept only true file descriptors) and forces protocol implementers to use various workarounds resulting in complex, non-standard and convoluted APIs. More generally, ability to create full-blown file descriptors for userspace-to-userspace signalling is missing. While eventfd(2) goes half the way towards this goal it has follwoing shorcomings: I. There's no way to signal POLLPRI, POLLHUP etc. II. There's no way to signal arbitrary combination of POLL* flags. Most notably, simultaneous !POLLIN and !POLLOUT, which is a perfectly valid combination for a network protocol (rx buffer is empty and tx buffer is full), cannot be signaled using eventfd. This patch implements new EFD_MASK flag which solves the above problems. Additionally, to provide a way to associate user-space state with eventfd object, it allows to attach user-space data to the file descriptor. The semantics of EFD_MASK are as follows: eventfd(2): If eventfd is created with EFD_MASK flag set, it is initialised in such a way as to signal no events on the file descriptor when it is polled on. 'initval' argument is ignored. write(2): User is allowed to write only buffers containing the following structure: struct efd_mask { __u32 events; __u64 data; }; The value of 'events' should be any combination of event flags as defined by poll(2) function (POLLIN, POLLOUT, POLLERR, POLLHUP etc.) Specified events will be signaled when polling (select, poll, epoll) on the eventfd is done later on. 'data' is opaque data that are not interpreted by eventfd object. read(2): User is allowed to read an efd_mask structure from the eventfd marked by EFD_MASK. Returned value shall be the last one written to the eventfd. select(2), poll(2) and similar: When polling on the eventfd marked by EFD_MASK flag, all the events specified in last written 'events' field shall be signaled. Signed-off-by: Martin Sustrik sust...@250bpm.com --- fs/eventfd.c | 93 ++-- include/linux/eventfd.h | 16 +--- include/uapi/linux/eventfd.h | 40 +++ 3 files changed, 123 insertions(+), 26 deletions(-) create mode 100644 include/uapi/linux/eventfd.h diff --git a/fs/eventfd.c b/fs/eventfd.c index 8d0c0df..11fb92a 100644 --- a/fs/eventfd.c +++ b/fs/eventfd.c @@ -2,6 +2,7 @@ * fs/eventfd.c * * Copyright (C) 2007 Davide Libenzi davi...@xmailserver.org + * Copyright (C) 2013 Martin Sustrik sust...@250bpm.com * */ @@ -22,18 +23,31 @@ #include linux/proc_fs.h #include linux/seq_file.h +#define EFD_SHARED_FCNTL_FLAGS (O_CLOEXEC | O_NONBLOCK) +#define EFD_FLAGS_SET (EFD_SHARED_FCNTL_FLAGS | EFD_SEMAPHORE | EFD_MASK) +#define EFD_MASK_VALID_EVENTS (POLLIN | POLLPRI | POLLOUT | POLLERR | POLLHUP) + struct eventfd_ctx { struct kref kref; wait_queue_head_t wqh; - /* -* Every time that a write(2) is performed on an eventfd, the -* value of the __u64 being written is added to count and a -* wakeup is performed on wqh. A read(2) will return the count -* value to userspace, and will reset count to zero. The kernel -* side eventfd_signal() also, adds to the count counter and -* issue a wakeup. -*/ - __u64 count; + union { + /* +* Every time that a write(2) is performed on an eventfd, the +* value of the __u64 being written is added to count and a +* wakeup is performed on wqh. A read(2) will return the +* count value to userspace, and will reset count to zero. +* The kernel side eventfd_signal() also, adds to the count +* counter and issue a wakeup. +*/ + __u64 count; + + /* +* When using eventfd in EFD_MASK mode this stracture stores the +* current events to be signaled on the eventfd (events member) +* along with opaque user-defined data (data member). +*/ + struct efd_mask mask; + }; unsigned int flags; }; @@ -55,6 +69,9 @@ __u64 eventfd_signal(struct eventfd_ctx *ctx, __u64 n) { unsigned long flags; + /* This function should never be used with eventfd in the mask mode. */ + BUG_ON(ctx-flags EFD_MASK); + spin_lock_irqsave(ctx-wqh.lock, flags); if (ULLONG_MAX - ctx-count n) n = ULLONG_MAX - ctx-count; @@ -124,6 +141,11 @@ static unsigned int eventfd_poll(struct file *file, poll_table *wait) smp_rmb(); count = ctx-count; + if (ctx-flags EFD_MASK) { + events = ctx-mask.events; + return