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[1/3] linux-user: Modify 'sendmmsg()' and 'recvmmsg()' implementation

Message ID 20200731190637.66698-2-Filip.Bozuta@syrmia.com
State New
Headers show
Series linux-user: Introducing support for 'recvmmsg_time64()' | expand

Commit Message

Filip Bozuta July 31, 2020, 7:06 p.m. UTC 
Implementations of 'sendmmsg()' and 'recvmmsg()' in 'syscall.c' use
a loop over a host command of 'sendmsg()' and 'recvmsg()' respectively
to send/receive individual messages from a socket. This patch changes
these implementations to use the host commands 'sendmmsg()' and 'recvmmsg()'
to send all messages without looping over 'sendmsg()' and 'recvmsg()'.

Implementation notes:

    Parts of code from 'do_sendrecvmsg_locked()', that are used to transfer
    values of 'struct msghdr' between host and target, were moved to separate
    functions 'target_to_host_msghdr()' and 'host_to_target_msghdr()'. These
    functions are used in 'do_sendrecvmmsg()' to transfer the data of each
    individual 'struct msghdr' from the 'msgvec' argument. Memory allocation
    for the 'iovec' field is done outside of these functions as to ensure that
    the memory is freed after the syscall execution.

Signed-off-by: Filip Bozuta <Filip.Bozuta@syrmia.com>
---
 linux-user/syscall.c | 243 ++++++++++++++++++++++++++++---------------
 1 file changed, 159 insertions(+), 84 deletions(-)

Comments

Laurent Vivier Aug. 24, 2020, 8:11 p.m. UTC | #1 
Le 31/07/2020 à 21:06, Filip Bozuta a écrit :
> Implementations of 'sendmmsg()' and 'recvmmsg()' in 'syscall.c' use
> a loop over a host command of 'sendmsg()' and 'recvmsg()' respectively
> to send/receive individual messages from a socket. This patch changes
> these implementations to use the host commands 'sendmmsg()' and 'recvmmsg()'
> to send all messages without looping over 'sendmsg()' and 'recvmsg()'.
> 
> Implementation notes:
> 
>     Parts of code from 'do_sendrecvmsg_locked()', that are used to transfer
>     values of 'struct msghdr' between host and target, were moved to separate
>     functions 'target_to_host_msghdr()' and 'host_to_target_msghdr()'. These
>     functions are used in 'do_sendrecvmmsg()' to transfer the data of each
>     individual 'struct msghdr' from the 'msgvec' argument. Memory allocation
>     for the 'iovec' field is done outside of these functions as to ensure that
>     the memory is freed after the syscall execution.
> 
> Signed-off-by: Filip Bozuta <Filip.Bozuta@syrmia.com>
> ---
>  linux-user/syscall.c | 243 ++++++++++++++++++++++++++++---------------
>  1 file changed, 159 insertions(+), 84 deletions(-)
> 

I'm sorry but after studying the changes needed I think it's better to
keep the existing code.

For instance, if we have a EFAULT (or EMSGSIZE) while reading the iovec
we must stop to send  data and exit with the error code.

Your code correctly manages the detection of the error and stops the
conversion of the iovec. Then it uses the converted iovecs with
sendmmsg() and recvmmsg(), but "ret" is overwritten and the error is lost.

So, in the end, and as it is done in kernel, the best is to loop around
sendmsg()... and this is what the existing code does.

Thanks,
Laurent
diff mbox series

Patch

diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index 05f03919ff..8cbefdb561 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -798,6 +798,10 @@  safe_syscall6(ssize_t, recvfrom, int, fd, void *, buf, size_t, len,
               int, flags, struct sockaddr *, addr, socklen_t *, addrlen)
 safe_syscall3(ssize_t, sendmsg, int, fd, const struct msghdr *, msg, int, flags)
 safe_syscall3(ssize_t, recvmsg, int, fd, struct msghdr *, msg, int, flags)
+safe_syscall4(int, sendmmsg, int, fd, struct mmsghdr *, msgvec,
+              unsigned int, vlen, int, flags)
+safe_syscall5(int, recvmmsg, int, fd, struct mmsghdr *, msgvec,
+              unsigned int, vlen, int, flags, struct timespec *, timeout)
 safe_syscall2(int, flock, int, fd, int, operation)
 #ifdef TARGET_NR_rt_sigtimedwait
 safe_syscall4(int, rt_sigtimedwait, const sigset_t *, these, siginfo_t *, uinfo,
@@ -3064,41 +3068,94 @@  static abi_long do_connect(int sockfd, abi_ulong target_addr,
     return get_errno(safe_connect(sockfd, addr, addrlen));
 }
 
-/* do_sendrecvmsg_locked() Must return target values and target errnos. */
-static abi_long do_sendrecvmsg_locked(int fd, struct target_msghdr *msgp,
-                                      int flags, int send)
+static abi_long target_to_host_msghdr(int fd, struct msghdr *host_msg,
+                                      struct target_msghdr *target_msg,
+                                      int send)
 {
-    abi_long ret, len;
-    struct msghdr msg;
-    abi_ulong count;
-    struct iovec *vec;
-    abi_ulong target_vec;
-
-    if (msgp->msg_name) {
-        msg.msg_namelen = tswap32(msgp->msg_namelen);
-        msg.msg_name = alloca(msg.msg_namelen+1);
-        ret = target_to_host_sockaddr(fd, msg.msg_name,
-                                      tswapal(msgp->msg_name),
-                                      msg.msg_namelen);
+    abi_long ret = 0;
+    if (target_msg->msg_name) {
+        host_msg->msg_namelen = tswap32(target_msg->msg_namelen);
+        host_msg->msg_name = alloca(host_msg->msg_namelen + 1);
+        ret = target_to_host_sockaddr(fd, host_msg->msg_name,
+                                      tswapal(target_msg->msg_name),
+                                      host_msg->msg_namelen);
         if (ret == -TARGET_EFAULT) {
-            /* For connected sockets msg_name and msg_namelen must
+            /*
+             * For connected sockets msg_name and msg_namelen must
              * be ignored, so returning EFAULT immediately is wrong.
              * Instead, pass a bad msg_name to the host kernel, and
              * let it decide whether to return EFAULT or not.
              */
-            msg.msg_name = (void *)-1;
+            host_msg->msg_name = (void *)-1;
+            ret = 0;
         } else if (ret) {
-            goto out2;
+            return ret;
         }
     } else {
-        msg.msg_name = NULL;
-        msg.msg_namelen = 0;
+        host_msg->msg_name = NULL;
+        host_msg->msg_namelen = 0;
+    }
+    host_msg->msg_controllen = 2 * tswapal(target_msg->msg_controllen);
+    host_msg->msg_control = alloca(host_msg->msg_controllen);
+    memset(host_msg->msg_control, 0, host_msg->msg_controllen);
+    host_msg->msg_flags = tswap32(target_msg->msg_flags);
+    if (send) {
+        if (fd_trans_target_to_host_data(fd)) {
+            void *host_iov_base;
+
+            host_iov_base = g_malloc(host_msg->msg_iov->iov_len);
+            memcpy(host_iov_base, host_msg->msg_iov->iov_base,
+                   host_msg->msg_iov->iov_len);
+            ret = fd_trans_target_to_host_data(fd)(host_iov_base,
+                                                   host_msg->msg_iov->iov_len);
+            if (ret >= 0) {
+                host_msg->msg_iov->iov_base = host_iov_base;
+                ret = 0;
+            }
+            g_free(host_iov_base);
+        } else {
+            ret = target_to_host_cmsg(host_msg, target_msg);
+        }
+    }
+    return ret;
+}
+
+static abi_long host_to_target_msghdr(int fd, struct target_msghdr *target_msg,
+                                      struct msghdr *host_msg, int len)
+{
+    abi_long ret;
+
+    if (fd_trans_host_to_target_data(fd)) {
+        ret = fd_trans_host_to_target_data(fd)(host_msg->msg_iov->iov_base,
+                                      MIN(host_msg->msg_iov->iov_len, len));
+    } else {
+        ret = host_to_target_cmsg(target_msg, host_msg);
+    }
+    if (!is_error(ret)) {
+        target_msg->msg_namelen = tswap32(host_msg->msg_namelen);
+        target_msg->msg_flags = tswap32(host_msg->msg_flags);
+        if (host_msg->msg_name != NULL && host_msg->msg_name != (void *)-1) {
+            ret = host_to_target_sockaddr(tswapal(target_msg->msg_name),
+                              host_msg->msg_name, host_msg->msg_namelen);
+            if (ret) {
+                return ret;
+            }
+        }
+        ret = len;
     }
-    msg.msg_controllen = 2 * tswapal(msgp->msg_controllen);
-    msg.msg_control = alloca(msg.msg_controllen);
-    memset(msg.msg_control, 0, msg.msg_controllen);
 
-    msg.msg_flags = tswap32(msgp->msg_flags);
+    return ret;
+}
+
+/* do_sendrecvmsg_locked() Must return target values and target errnos. */
+static abi_long do_sendrecvmsg_locked(int fd, struct target_msghdr *msgp,
+                                      int flags, int send)
+{
+    abi_long ret;
+    struct msghdr msg;
+    abi_ulong count;
+    struct iovec *vec;
+    abi_ulong target_vec;
 
     count = tswapal(msgp->msg_iovlen);
     target_vec = tswapal(msgp->msg_iov);
@@ -3120,48 +3177,18 @@  static abi_long do_sendrecvmsg_locked(int fd, struct target_msghdr *msgp,
     msg.msg_iovlen = count;
     msg.msg_iov = vec;
 
-    if (send) {
-        if (fd_trans_target_to_host_data(fd)) {
-            void *host_msg;
+    ret = target_to_host_msghdr(fd, &msg, msgp, send);
 
-            host_msg = g_malloc(msg.msg_iov->iov_len);
-            memcpy(host_msg, msg.msg_iov->iov_base, msg.msg_iov->iov_len);
-            ret = fd_trans_target_to_host_data(fd)(host_msg,
-                                                   msg.msg_iov->iov_len);
-            if (ret >= 0) {
-                msg.msg_iov->iov_base = host_msg;
-                ret = get_errno(safe_sendmsg(fd, &msg, flags));
-            }
-            g_free(host_msg);
-        } else {
-            ret = target_to_host_cmsg(&msg, msgp);
-            if (ret == 0) {
-                ret = get_errno(safe_sendmsg(fd, &msg, flags));
-            }
-        }
+    if (ret) {
+        goto out;
+    }
+
+    if (send) {
+        ret = get_errno(safe_sendmsg(fd, &msg, flags));
     } else {
         ret = get_errno(safe_recvmsg(fd, &msg, flags));
         if (!is_error(ret)) {
-            len = ret;
-            if (fd_trans_host_to_target_data(fd)) {
-                ret = fd_trans_host_to_target_data(fd)(msg.msg_iov->iov_base,
-                                               MIN(msg.msg_iov->iov_len, len));
-            } else {
-                ret = host_to_target_cmsg(msgp, &msg);
-            }
-            if (!is_error(ret)) {
-                msgp->msg_namelen = tswap32(msg.msg_namelen);
-                msgp->msg_flags = tswap32(msg.msg_flags);
-                if (msg.msg_name != NULL && msg.msg_name != (void *)-1) {
-                    ret = host_to_target_sockaddr(tswapal(msgp->msg_name),
-                                    msg.msg_name, msg.msg_namelen);
-                    if (ret) {
-                        goto out;
-                    }
-                }
-
-                ret = len;
-            }
+            ret = host_to_target_msghdr(fd, msgp, &msg, ret);
         }
     }
 
@@ -3188,50 +3215,98 @@  static abi_long do_sendrecvmsg(int fd, abi_ulong target_msg,
     return ret;
 }
 
-/* We don't rely on the C library to have sendmmsg/recvmmsg support,
- * so it might not have this *mmsg-specific flag either.
- */
-#ifndef MSG_WAITFORONE
-#define MSG_WAITFORONE 0x10000
-#endif
-
-static abi_long do_sendrecvmmsg(int fd, abi_ulong target_msgvec,
+static abi_long do_sendrecvmmsg(int fd, abi_ulong target_msgvec_addr,
                                 unsigned int vlen, unsigned int flags,
                                 int send)
 {
-    struct target_mmsghdr *mmsgp;
+    struct mmsghdr *host_msgvec;
+    struct target_mmsghdr *target_msgvec;
     abi_long ret = 0;
+    int num_sentrecv = 0;
+    int num_iovec = 0;
+    abi_ulong iovlen = 0;
+    struct iovec *host_iovec;
+    abi_ulong target_iovec;
     int i;
 
     if (vlen > UIO_MAXIOV) {
         vlen = UIO_MAXIOV;
     }
 
-    mmsgp = lock_user(VERIFY_WRITE, target_msgvec, sizeof(*mmsgp) * vlen, 1);
-    if (!mmsgp) {
+    target_msgvec = lock_user(VERIFY_WRITE, target_msgvec_addr,
+                              sizeof(target_msgvec) * vlen, 1);
+    if (!target_msgvec) {
         return -TARGET_EFAULT;
     }
 
+    host_msgvec = alloca(sizeof(*host_msgvec) * vlen);
+
     for (i = 0; i < vlen; i++) {
-        ret = do_sendrecvmsg_locked(fd, &mmsgp[i].msg_hdr, flags, send);
+
+        iovlen = tswapal(target_msgvec[i].msg_hdr.msg_iovlen);
+        target_iovec = tswapal(target_msgvec[i].msg_hdr.msg_iov);
+
+        if (iovlen > IOV_MAX) {
+            ret = -TARGET_EMSGSIZE;
+            break;
+         }
+         host_iovec = lock_iovec(send ? VERIFY_READ : VERIFY_WRITE,
+                                 target_iovec, iovlen, send);
+
+        if (host_iovec == NULL) {
+            ret = -host_to_target_errno(errno);
+            break;
+        }
+
+        num_iovec++;
+
+        host_msgvec[i].msg_hdr.msg_iovlen = iovlen;
+        host_msgvec[i].msg_hdr.msg_iov = host_iovec;
+
+        ret = target_to_host_msghdr(fd, &host_msgvec[i].msg_hdr,
+                                    &target_msgvec[i].msg_hdr, send);
+
         if (is_error(ret)) {
             break;
         }
-        mmsgp[i].msg_len = tswap32(ret);
-        /* MSG_WAITFORONE turns on MSG_DONTWAIT after one packet */
-        if (flags & MSG_WAITFORONE) {
-            flags |= MSG_DONTWAIT;
+    }
+
+    if (i > 0) {
+        if (send) {
+            ret = get_errno(safe_sendmmsg(fd, host_msgvec, i, flags));
+        } else {
+            ret = get_errno(safe_recvmmsg(fd, host_msgvec, i, flags, NULL));
+        }
+    }
+
+    if (!is_error(ret)) {
+        num_sentrecv = ret;
+        for (i = 0; i < num_sentrecv; i++) {
+            if (!send) {
+                ret = host_to_target_msghdr(fd, &target_msgvec[i].msg_hdr,
+                                            &host_msgvec[i].msg_hdr,
+                                            host_msgvec[i].msg_len);
+                if (is_error(ret)) {
+                    num_sentrecv = i;
+                    break;
+                }
+            }
+            target_msgvec[i].msg_len = tswap32(host_msgvec[i].msg_len);
         }
     }
 
-    unlock_user(mmsgp, target_msgvec, sizeof(*mmsgp) * i);
+    for (i = 0; i < num_iovec; i++) {
+        target_iovec = tswapal(target_msgvec[i].msg_hdr.msg_iov);
+        unlock_iovec(host_msgvec[i].msg_hdr.msg_iov,
+                     target_iovec, iovlen, !send);
+    }
+
+    unlock_user(target_msgvec, target_msgvec_addr, sizeof(*target_msgvec) * i);
 
-    /* Return number of datagrams sent if we sent any at all;
-     * otherwise return the error.
-     */
-    if (i) {
-        return i;
+    if (num_sentrecv) {
+        return num_sentrecv;
     }
+
     return ret;
 }