| Message ID | 20240708210405.870930-3-zijianzhang@bytedance.com (mailing list archive) |
|---|---|
| State | Changes Requested |
| Delegated to: | Netdev Maintainers |
| Headers | show |
| Series | net: A lightweight zero-copy notification | expand |
On Mon, Jul 08, 2024 at 09:04:04PM +0000, zijianzhang@bytedance.com wrote: > From: Zijian Zhang <zijianzhang@bytedance.com> > > The MSG_ZEROCOPY flag enables copy avoidance for socket send calls. > However, zerocopy is not a free lunch. Apart from the management of user > pages, the combination of poll + recvmsg to receive notifications incurs > unignorable overhead in the applications. We try to mitigate this overhead > with a new notification mechanism based on msg_control. Leveraging the > general framework to copy cmsgs to the user space, we copy zerocopy > notifications to the user upon returning of sendmsgs. > > Signed-off-by: Zijian Zhang <zijianzhang@bytedance.com> > Signed-off-by: Xiaochun Lu <xiaochun.lu@bytedance.com> > --- > arch/alpha/include/uapi/asm/socket.h | 2 ++ > arch/mips/include/uapi/asm/socket.h | 2 ++ > arch/parisc/include/uapi/asm/socket.h | 2 ++ > arch/sparc/include/uapi/asm/socket.h | 2 ++ > include/linux/socket.h | 2 +- > include/uapi/asm-generic/socket.h | 2 ++ > include/uapi/linux/socket.h | 13 ++++++++ > net/core/sock.c | 46 +++++++++++++++++++++++++++ > 8 files changed, 70 insertions(+), 1 deletion(-) > > diff --git a/arch/alpha/include/uapi/asm/socket.h b/arch/alpha/include/uapi/asm/socket.h > index e94f621903fe..7c32d9dbe47f 100644 > --- a/arch/alpha/include/uapi/asm/socket.h > +++ b/arch/alpha/include/uapi/asm/socket.h > @@ -140,6 +140,8 @@ > #define SO_PASSPIDFD 76 > #define SO_PEERPIDFD 77 > > +#define SCM_ZC_NOTIFICATION 78 > + > #if !defined(__KERNEL__) > > #if __BITS_PER_LONG == 64 > diff --git a/arch/mips/include/uapi/asm/socket.h b/arch/mips/include/uapi/asm/socket.h > index 60ebaed28a4c..3f7fade998cb 100644 > --- a/arch/mips/include/uapi/asm/socket.h > +++ b/arch/mips/include/uapi/asm/socket.h > @@ -151,6 +151,8 @@ > #define SO_PASSPIDFD 76 > #define SO_PEERPIDFD 77 > > +#define SCM_ZC_NOTIFICATION 78 > + > #if !defined(__KERNEL__) > > #if __BITS_PER_LONG == 64 > diff --git a/arch/parisc/include/uapi/asm/socket.h b/arch/parisc/include/uapi/asm/socket.h > index be264c2b1a11..77f5bee0fdc9 100644 > --- a/arch/parisc/include/uapi/asm/socket.h > +++ b/arch/parisc/include/uapi/asm/socket.h > @@ -132,6 +132,8 @@ > #define SO_PASSPIDFD 0x404A > #define SO_PEERPIDFD 0x404B > > +#define SCM_ZC_NOTIFICATION 0x404C > + > #if !defined(__KERNEL__) > > #if __BITS_PER_LONG == 64 > diff --git a/arch/sparc/include/uapi/asm/socket.h b/arch/sparc/include/uapi/asm/socket.h > index 682da3714686..eb44fc515b45 100644 > --- a/arch/sparc/include/uapi/asm/socket.h > +++ b/arch/sparc/include/uapi/asm/socket.h > @@ -133,6 +133,8 @@ > #define SO_PASSPIDFD 0x0055 > #define SO_PEERPIDFD 0x0056 > > +#define SCM_ZC_NOTIFICATION 0x0057 > + > #if !defined(__KERNEL__) > > > diff --git a/include/linux/socket.h b/include/linux/socket.h > index 75461812a7a3..6f1b791e2de8 100644 > --- a/include/linux/socket.h > +++ b/include/linux/socket.h > @@ -171,7 +171,7 @@ static inline struct cmsghdr * cmsg_nxthdr (struct msghdr *__msg, struct cmsghdr > > static inline bool cmsg_copy_to_user(struct cmsghdr *__cmsg) > { > - return 0; > + return __cmsg->cmsg_type == SCM_ZC_NOTIFICATION; > } > > static inline size_t msg_data_left(struct msghdr *msg) > diff --git a/include/uapi/asm-generic/socket.h b/include/uapi/asm-generic/socket.h > index 8ce8a39a1e5f..02e9159c7944 100644 > --- a/include/uapi/asm-generic/socket.h > +++ b/include/uapi/asm-generic/socket.h > @@ -135,6 +135,8 @@ > #define SO_PASSPIDFD 76 > #define SO_PEERPIDFD 77 > > +#define SCM_ZC_NOTIFICATION 78 > + > #if !defined(__KERNEL__) > > #if __BITS_PER_LONG == 64 || (defined(__x86_64__) && defined(__ILP32__)) > diff --git a/include/uapi/linux/socket.h b/include/uapi/linux/socket.h > index d3fcd3b5ec53..ab361f30f3a6 100644 > --- a/include/uapi/linux/socket.h > +++ b/include/uapi/linux/socket.h > @@ -2,6 +2,8 @@ > #ifndef _UAPI_LINUX_SOCKET_H > #define _UAPI_LINUX_SOCKET_H > > +#include <linux/types.h> > + > /* > * Desired design of maximum size and alignment (see RFC2553) > */ > @@ -35,4 +37,15 @@ struct __kernel_sockaddr_storage { > #define SOCK_TXREHASH_DISABLED 0 > #define SOCK_TXREHASH_ENABLED 1 > > +struct zc_info_elem { > + __u32 lo; > + __u32 hi; > + __u8 zerocopy; Some docs please on what each of these are, if possible. Sorry if the repeated requests are annoying. In particular I'm a bit confused why the zerocopy field is there. Looking at the code, is this always set to 1? > +}; > + > +struct zc_info { > + __u32 size; > + struct zc_info_elem arr[]; > +}; > + > #endif /* _UAPI_LINUX_SOCKET_H */ > diff --git a/net/core/sock.c b/net/core/sock.c > index efb30668dac3..e0b5162233d3 100644 > --- a/net/core/sock.c > +++ b/net/core/sock.c > @@ -2863,6 +2863,52 @@ int __sock_cmsg_send(struct sock *sk, struct msghdr *msg, struct cmsghdr *cmsg, > case SCM_RIGHTS: > case SCM_CREDENTIALS: > break; > + case SCM_ZC_NOTIFICATION: { > + struct zc_info *zc_info = CMSG_DATA(cmsg); > + struct zc_info_elem *zc_info_arr; > + struct sock_exterr_skb *serr; > + int cmsg_data_len, i = 0; > + struct sk_buff_head *q; > + unsigned long flags; > + struct sk_buff *skb; > + u32 zc_info_size; > + > + if (!sock_flag(sk, SOCK_ZEROCOPY) || sk->sk_family == PF_RDS) > + return -EINVAL; > + > + cmsg_data_len = cmsg->cmsg_len - sizeof(struct cmsghdr); > + if (cmsg_data_len < sizeof(struct zc_info)) > + return -EINVAL; > + > + zc_info_size = zc_info->size; > + zc_info_arr = zc_info->arr; Annoying nit: To be honest zc_info->size isn't much longer to type than zc_info_size, so I would have not added local variables. > + if (cmsg_data_len != sizeof(struct zc_info) + > + zc_info_size * sizeof(struct zc_info_elem)) > + return -EINVAL; > + > + q = &sk->sk_error_queue; > + spin_lock_irqsave(&q->lock, flags); > + skb = skb_peek(q); > + while (skb && i < zc_info_size) { > + struct sk_buff *skb_next = skb_peek_next(skb, q); > + > + serr = SKB_EXT_ERR(skb); > + if (serr->ee.ee_errno == 0 && > + serr->ee.ee_origin == SO_EE_ORIGIN_ZEROCOPY) { > + zc_info_arr[i].hi = serr->ee.ee_data; > + zc_info_arr[i].lo = serr->ee.ee_info; > + zc_info_arr[i].zerocopy = !(serr->ee.ee_code > + & SO_EE_CODE_ZEROCOPY_COPIED); > + __skb_unlink(skb, q); > + consume_skb(skb); > + i++; > + } > + skb = skb_next; > + } > + spin_unlock_irqrestore(&q->lock, flags); I wonder if you should drop the spin lock in the middle of this loop somehow, otherwise you may end up spinning for a very long time while the spinlock held and irq disabled. IIRC zc_info_size is user input, right? Maybe you should limit zc_info_size to 16 entries or something. So the user doesn't end up passing 100000 as zc_info_size and making the kernel loop for a long time here. > + zc_info->size = i; > + break; > + } > default: > return -EINVAL; > } > -- > 2.20.1 >
On 7/25/24 2:59 PM, Mina Almasry wrote: > On Mon, Jul 08, 2024 at 09:04:04PM +0000, zijianzhang@bytedance.com wrote: >> From: Zijian Zhang <zijianzhang@bytedance.com> >> >> The MSG_ZEROCOPY flag enables copy avoidance for socket send calls. >> However, zerocopy is not a free lunch. Apart from the management of user >> pages, the combination of poll + recvmsg to receive notifications incurs >> unignorable overhead in the applications. We try to mitigate this overhead >> with a new notification mechanism based on msg_control. Leveraging the >> general framework to copy cmsgs to the user space, we copy zerocopy >> notifications to the user upon returning of sendmsgs. >> >> Signed-off-by: Zijian Zhang <zijianzhang@bytedance.com> >> Signed-off-by: Xiaochun Lu <xiaochun.lu@bytedance.com> >> --- >> arch/alpha/include/uapi/asm/socket.h | 2 ++ >> arch/mips/include/uapi/asm/socket.h | 2 ++ >> arch/parisc/include/uapi/asm/socket.h | 2 ++ >> arch/sparc/include/uapi/asm/socket.h | 2 ++ >> include/linux/socket.h | 2 +- >> include/uapi/asm-generic/socket.h | 2 ++ >> include/uapi/linux/socket.h | 13 ++++++++ >> net/core/sock.c | 46 +++++++++++++++++++++++++++ >> 8 files changed, 70 insertions(+), 1 deletion(-) >> >> diff --git a/arch/alpha/include/uapi/asm/socket.h b/arch/alpha/include/uapi/asm/socket.h >> index e94f621903fe..7c32d9dbe47f 100644 >> --- a/arch/alpha/include/uapi/asm/socket.h >> +++ b/arch/alpha/include/uapi/asm/socket.h >> @@ -140,6 +140,8 @@ >> #define SO_PASSPIDFD 76 >> #define SO_PEERPIDFD 77 >> >> +#define SCM_ZC_NOTIFICATION 78 >> + >> #if !defined(__KERNEL__) >> >> #if __BITS_PER_LONG == 64 >> diff --git a/arch/mips/include/uapi/asm/socket.h b/arch/mips/include/uapi/asm/socket.h >> index 60ebaed28a4c..3f7fade998cb 100644 >> --- a/arch/mips/include/uapi/asm/socket.h >> +++ b/arch/mips/include/uapi/asm/socket.h >> @@ -151,6 +151,8 @@ >> #define SO_PASSPIDFD 76 >> #define SO_PEERPIDFD 77 >> >> +#define SCM_ZC_NOTIFICATION 78 >> + >> #if !defined(__KERNEL__) >> >> #if __BITS_PER_LONG == 64 >> diff --git a/arch/parisc/include/uapi/asm/socket.h b/arch/parisc/include/uapi/asm/socket.h >> index be264c2b1a11..77f5bee0fdc9 100644 >> --- a/arch/parisc/include/uapi/asm/socket.h >> +++ b/arch/parisc/include/uapi/asm/socket.h >> @@ -132,6 +132,8 @@ >> #define SO_PASSPIDFD 0x404A >> #define SO_PEERPIDFD 0x404B >> >> +#define SCM_ZC_NOTIFICATION 0x404C >> + >> #if !defined(__KERNEL__) >> >> #if __BITS_PER_LONG == 64 >> diff --git a/arch/sparc/include/uapi/asm/socket.h b/arch/sparc/include/uapi/asm/socket.h >> index 682da3714686..eb44fc515b45 100644 >> --- a/arch/sparc/include/uapi/asm/socket.h >> +++ b/arch/sparc/include/uapi/asm/socket.h >> @@ -133,6 +133,8 @@ >> #define SO_PASSPIDFD 0x0055 >> #define SO_PEERPIDFD 0x0056 >> >> +#define SCM_ZC_NOTIFICATION 0x0057 >> + >> #if !defined(__KERNEL__) >> >> >> diff --git a/include/linux/socket.h b/include/linux/socket.h >> index 75461812a7a3..6f1b791e2de8 100644 >> --- a/include/linux/socket.h >> +++ b/include/linux/socket.h >> @@ -171,7 +171,7 @@ static inline struct cmsghdr * cmsg_nxthdr (struct msghdr *__msg, struct cmsghdr >> >> static inline bool cmsg_copy_to_user(struct cmsghdr *__cmsg) >> { >> - return 0; >> + return __cmsg->cmsg_type == SCM_ZC_NOTIFICATION; >> } >> >> static inline size_t msg_data_left(struct msghdr *msg) >> diff --git a/include/uapi/asm-generic/socket.h b/include/uapi/asm-generic/socket.h >> index 8ce8a39a1e5f..02e9159c7944 100644 >> --- a/include/uapi/asm-generic/socket.h >> +++ b/include/uapi/asm-generic/socket.h >> @@ -135,6 +135,8 @@ >> #define SO_PASSPIDFD 76 >> #define SO_PEERPIDFD 77 >> >> +#define SCM_ZC_NOTIFICATION 78 >> + >> #if !defined(__KERNEL__) >> >> #if __BITS_PER_LONG == 64 || (defined(__x86_64__) && defined(__ILP32__)) >> diff --git a/include/uapi/linux/socket.h b/include/uapi/linux/socket.h >> index d3fcd3b5ec53..ab361f30f3a6 100644 >> --- a/include/uapi/linux/socket.h >> +++ b/include/uapi/linux/socket.h >> @@ -2,6 +2,8 @@ >> #ifndef _UAPI_LINUX_SOCKET_H >> #define _UAPI_LINUX_SOCKET_H >> >> +#include <linux/types.h> >> + >> /* >> * Desired design of maximum size and alignment (see RFC2553) >> */ >> @@ -35,4 +37,15 @@ struct __kernel_sockaddr_storage { >> #define SOCK_TXREHASH_DISABLED 0 >> #define SOCK_TXREHASH_ENABLED 1 >> >> +struct zc_info_elem { >> + __u32 lo; >> + __u32 hi; >> + __u8 zerocopy; > > Some docs please on what each of these are, if possible. Sorry if the repeated > requests are annoying. > > In particular I'm a bit confused why the zerocopy field is there. Looking at > the code, is this always set to 1? > ``` hi = serr->ee_data; lo = serr->ee_info; zerocopy = !(serr->ee_code & SO_EE_CODE_ZEROCOPY_COPIED); ``` In the original method, the above code means one notification for sendmsg id [lo, hi], with zerocopy=n/y to denote if the zerocopy is reverted back to copy. So the zerocopy field aligns the same meaning of !(serr->ee_code & SO_EE_CODE_ZEROCOPY_COPIED) in the original method. Sorry for the confusion, I will add more docs to explain it. >> +}; >> + >> +struct zc_info { >> + __u32 size; >> + struct zc_info_elem arr[]; >> +}; >> + >> #endif /* _UAPI_LINUX_SOCKET_H */ >> diff --git a/net/core/sock.c b/net/core/sock.c >> index efb30668dac3..e0b5162233d3 100644 >> --- a/net/core/sock.c >> +++ b/net/core/sock.c >> @@ -2863,6 +2863,52 @@ int __sock_cmsg_send(struct sock *sk, struct msghdr *msg, struct cmsghdr *cmsg, >> case SCM_RIGHTS: >> case SCM_CREDENTIALS: >> break; >> + case SCM_ZC_NOTIFICATION: { >> + struct zc_info *zc_info = CMSG_DATA(cmsg); >> + struct zc_info_elem *zc_info_arr; >> + struct sock_exterr_skb *serr; >> + int cmsg_data_len, i = 0; >> + struct sk_buff_head *q; >> + unsigned long flags; >> + struct sk_buff *skb; >> + u32 zc_info_size; >> + >> + if (!sock_flag(sk, SOCK_ZEROCOPY) || sk->sk_family == PF_RDS) >> + return -EINVAL; >> + >> + cmsg_data_len = cmsg->cmsg_len - sizeof(struct cmsghdr); >> + if (cmsg_data_len < sizeof(struct zc_info)) >> + return -EINVAL; >> + >> + zc_info_size = zc_info->size; >> + zc_info_arr = zc_info->arr; > > Annoying nit: To be honest zc_info->size isn't much longer to type than > zc_info_size, so I would have not added local variables. > Agree, nice catch! >> + if (cmsg_data_len != sizeof(struct zc_info) + >> + zc_info_size * sizeof(struct zc_info_elem)) >> + return -EINVAL; >> + >> + q = &sk->sk_error_queue; >> + spin_lock_irqsave(&q->lock, flags); >> + skb = skb_peek(q); >> + while (skb && i < zc_info_size) { >> + struct sk_buff *skb_next = skb_peek_next(skb, q); >> + >> + serr = SKB_EXT_ERR(skb); >> + if (serr->ee.ee_errno == 0 && >> + serr->ee.ee_origin == SO_EE_ORIGIN_ZEROCOPY) { >> + zc_info_arr[i].hi = serr->ee.ee_data; >> + zc_info_arr[i].lo = serr->ee.ee_info; >> + zc_info_arr[i].zerocopy = !(serr->ee.ee_code >> + & SO_EE_CODE_ZEROCOPY_COPIED); >> + __skb_unlink(skb, q); >> + consume_skb(skb); >> + i++; >> + } >> + skb = skb_next; >> + } >> + spin_unlock_irqrestore(&q->lock, flags); > > I wonder if you should drop the spin lock in the middle of this loop somehow, > otherwise you may end up spinning for a very long time while the spinlock held > and irq disabled. > > IIRC zc_info_size is user input, right? Maybe you should limit zc_info_size to > 16 entries or something. So the user doesn't end up passing 100000 as > zc_info_size and making the kernel loop for a long time here. > Thanks for the suggestion, totally agree, I should limit the zc_info_size. >> + zc_info->size = i; >> + break; >> + } >> default: >> return -EINVAL; >> } >> -- >> 2.20.1 >>
diff --git a/arch/alpha/include/uapi/asm/socket.h b/arch/alpha/include/uapi/asm/socket.h index e94f621903fe..7c32d9dbe47f 100644 --- a/arch/alpha/include/uapi/asm/socket.h +++ b/arch/alpha/include/uapi/asm/socket.h @@ -140,6 +140,8 @@ #define SO_PASSPIDFD 76 #define SO_PEERPIDFD 77 +#define SCM_ZC_NOTIFICATION 78 + #if !defined(__KERNEL__) #if __BITS_PER_LONG == 64 diff --git a/arch/mips/include/uapi/asm/socket.h b/arch/mips/include/uapi/asm/socket.h index 60ebaed28a4c..3f7fade998cb 100644 --- a/arch/mips/include/uapi/asm/socket.h +++ b/arch/mips/include/uapi/asm/socket.h @@ -151,6 +151,8 @@ #define SO_PASSPIDFD 76 #define SO_PEERPIDFD 77 +#define SCM_ZC_NOTIFICATION 78 + #if !defined(__KERNEL__) #if __BITS_PER_LONG == 64 diff --git a/arch/parisc/include/uapi/asm/socket.h b/arch/parisc/include/uapi/asm/socket.h index be264c2b1a11..77f5bee0fdc9 100644 --- a/arch/parisc/include/uapi/asm/socket.h +++ b/arch/parisc/include/uapi/asm/socket.h @@ -132,6 +132,8 @@ #define SO_PASSPIDFD 0x404A #define SO_PEERPIDFD 0x404B +#define SCM_ZC_NOTIFICATION 0x404C + #if !defined(__KERNEL__) #if __BITS_PER_LONG == 64 diff --git a/arch/sparc/include/uapi/asm/socket.h b/arch/sparc/include/uapi/asm/socket.h index 682da3714686..eb44fc515b45 100644 --- a/arch/sparc/include/uapi/asm/socket.h +++ b/arch/sparc/include/uapi/asm/socket.h @@ -133,6 +133,8 @@ #define SO_PASSPIDFD 0x0055 #define SO_PEERPIDFD 0x0056 +#define SCM_ZC_NOTIFICATION 0x0057 + #if !defined(__KERNEL__) diff --git a/include/linux/socket.h b/include/linux/socket.h index 75461812a7a3..6f1b791e2de8 100644 --- a/include/linux/socket.h +++ b/include/linux/socket.h @@ -171,7 +171,7 @@ static inline struct cmsghdr * cmsg_nxthdr (struct msghdr *__msg, struct cmsghdr static inline bool cmsg_copy_to_user(struct cmsghdr *__cmsg) { - return 0; + return __cmsg->cmsg_type == SCM_ZC_NOTIFICATION; } static inline size_t msg_data_left(struct msghdr *msg) diff --git a/include/uapi/asm-generic/socket.h b/include/uapi/asm-generic/socket.h index 8ce8a39a1e5f..02e9159c7944 100644 --- a/include/uapi/asm-generic/socket.h +++ b/include/uapi/asm-generic/socket.h @@ -135,6 +135,8 @@ #define SO_PASSPIDFD 76 #define SO_PEERPIDFD 77 +#define SCM_ZC_NOTIFICATION 78 + #if !defined(__KERNEL__) #if __BITS_PER_LONG == 64 || (defined(__x86_64__) && defined(__ILP32__)) diff --git a/include/uapi/linux/socket.h b/include/uapi/linux/socket.h index d3fcd3b5ec53..ab361f30f3a6 100644 --- a/include/uapi/linux/socket.h +++ b/include/uapi/linux/socket.h @@ -2,6 +2,8 @@ #ifndef _UAPI_LINUX_SOCKET_H #define _UAPI_LINUX_SOCKET_H +#include <linux/types.h> + /* * Desired design of maximum size and alignment (see RFC2553) */ @@ -35,4 +37,15 @@ struct __kernel_sockaddr_storage { #define SOCK_TXREHASH_DISABLED 0 #define SOCK_TXREHASH_ENABLED 1 +struct zc_info_elem { + __u32 lo; + __u32 hi; + __u8 zerocopy; +}; + +struct zc_info { + __u32 size; + struct zc_info_elem arr[]; +}; + #endif /* _UAPI_LINUX_SOCKET_H */ diff --git a/net/core/sock.c b/net/core/sock.c index efb30668dac3..e0b5162233d3 100644 --- a/net/core/sock.c +++ b/net/core/sock.c @@ -2863,6 +2863,52 @@ int __sock_cmsg_send(struct sock *sk, struct msghdr *msg, struct cmsghdr *cmsg, case SCM_RIGHTS: case SCM_CREDENTIALS: break; + case SCM_ZC_NOTIFICATION: { + struct zc_info *zc_info = CMSG_DATA(cmsg); + struct zc_info_elem *zc_info_arr; + struct sock_exterr_skb *serr; + int cmsg_data_len, i = 0; + struct sk_buff_head *q; + unsigned long flags; + struct sk_buff *skb; + u32 zc_info_size; + + if (!sock_flag(sk, SOCK_ZEROCOPY) || sk->sk_family == PF_RDS) + return -EINVAL; + + cmsg_data_len = cmsg->cmsg_len - sizeof(struct cmsghdr); + if (cmsg_data_len < sizeof(struct zc_info)) + return -EINVAL; + + zc_info_size = zc_info->size; + zc_info_arr = zc_info->arr; + if (cmsg_data_len != sizeof(struct zc_info) + + zc_info_size * sizeof(struct zc_info_elem)) + return -EINVAL; + + q = &sk->sk_error_queue; + spin_lock_irqsave(&q->lock, flags); + skb = skb_peek(q); + while (skb && i < zc_info_size) { + struct sk_buff *skb_next = skb_peek_next(skb, q); + + serr = SKB_EXT_ERR(skb); + if (serr->ee.ee_errno == 0 && + serr->ee.ee_origin == SO_EE_ORIGIN_ZEROCOPY) { + zc_info_arr[i].hi = serr->ee.ee_data; + zc_info_arr[i].lo = serr->ee.ee_info; + zc_info_arr[i].zerocopy = !(serr->ee.ee_code + & SO_EE_CODE_ZEROCOPY_COPIED); + __skb_unlink(skb, q); + consume_skb(skb); + i++; + } + skb = skb_next; + } + spin_unlock_irqrestore(&q->lock, flags); + zc_info->size = i; + break; + } default: return -EINVAL; }