Give sendfile(2) a SF_SYNC flag which makes it wait until all mbufs

referencing the files VM pages are returned from the network stack,
making changes to the file safe.

This flag does not guarantee that the data has been transmitted to the
other end.

1 files changed, 42 insertions, 1 deletions

diff --git a/sys/kern/uipc_syscalls.c b/sys/kern/uipc_syscalls.c
index beca062..789276e 100644
--- a/sys/kern/uipc_syscalls.c
+++ b/sys/kern/uipc_syscalls.c
@@ -1660,6 +1660,14 @@ getsockaddr(namp, uaddr, len)
 	return (error);
 }
 
+#include <sys/condvar.h>
+
+struct sendfile_sync {
+	struct mtx	mtx;
+	struct cv	cv;
+	unsigned 	count;
+};
+
 /*
  * Detach mapped page and release resources back to the system.
  */
@@ -1667,6 +1675,7 @@ void
 sf_buf_mext(void *addr, void *args)
 {
 	vm_page_t m;
+	struct sendfile_sync *sfs;
 
 	m = sf_buf_page(args);
 	sf_buf_free(args);
@@ -1680,6 +1689,14 @@ sf_buf_mext(void *addr, void *args)
 	if (m->wire_count == 0 && m->object == NULL)
 		vm_page_free(m);
 	vm_page_unlock_queues();
+	if (addr == NULL)
+		return;
+	sfs = addr;
+	mtx_lock(&sfs->mtx);
+	KASSERT(sfs->count> 0, ("Sendfile sync botchup count == 0"));
+	if (--sfs->count == 0)
+		cv_signal(&sfs->cv);
+	mtx_unlock(&sfs->mtx);
 }
 
 /*
@@ -1767,6 +1784,7 @@ kern_sendfile(struct thread *td, struct sendfile_args *uap,
 	off_t off, xfsize, fsbytes = 0, sbytes = 0, rem = 0;
 	int error, hdrlen = 0, mnw = 0;
 	int vfslocked;
+	struct sendfile_sync *sfs = NULL;
 
 	/*
 	 * The file descriptor must be a regular file and have a
@@ -1829,6 +1847,13 @@ kern_sendfile(struct thread *td, struct sendfile_args *uap,
 	if (uap->flags & SF_MNOWAIT)
 		mnw = 1;
 
+	if (uap->flags & SF_SYNC) {
+		sfs = malloc(sizeof *sfs, M_TEMP, M_WAITOK);
+		memset(sfs, 0, sizeof *sfs);
+		mtx_init(&sfs->mtx, "sendfile", MTX_DEF, 0);
+		cv_init(&sfs->cv, "sendfile");
+	}
+
 #ifdef MAC
 	SOCK_LOCK(so);
 	error = mac_socket_check_send(td->td_ucred, so);
@@ -2099,7 +2124,7 @@ retry_space:
 				break;
 			}
 			MEXTADD(m0, sf_buf_kva(sf), PAGE_SIZE, sf_buf_mext,
-			    (void*)sf_buf_kva(sf), sf, M_RDONLY, EXT_SFBUF);
+			    sfs, sf, M_RDONLY, EXT_SFBUF);
 			m0->m_data = (char *)sf_buf_kva(sf) + pgoff;
 			m0->m_len = xfsize;
 
@@ -2112,6 +2137,12 @@ retry_space:
 			/* Keep track of bits processed. */
 			loopbytes += xfsize;
 			off += xfsize;
+
+			if (sfs != NULL) {
+				mtx_lock(&sfs->mtx);
+				sfs->count++;
+				mtx_unlock(&sfs->mtx);
+			}
 		}
 
 		/* Add the buffer chain to the socket buffer. */
@@ -2190,6 +2221,16 @@ out:
 	if (m)
 		m_freem(m);
 
+	if (sfs != NULL) {
+		mtx_lock(&sfs->mtx);
+		if (sfs->count != 0)
+			cv_wait(&sfs->cv, &sfs->mtx);
+		KASSERT(sfs->count == 0, ("sendfile sync still busy"));
+		cv_destroy(&sfs->cv);
+		mtx_destroy(&sfs->mtx);
+		free(sfs, M_TEMP);
+	}
+
 	if (error == ERESTART)
 		error = EINTR;