linux-kernel - [PATCH v2 2/3] userfaultfd: selftest: generalize read and poll

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Date:   Sun, 30 Sep 2018 15:42:58 +0800
From:   Peter Xu <peterx@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     Shuah Khan <shuah@...nel.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Jerome Glisse <jglisse@...hat.com>, peterx@...hat.com,
        linux-mm@...ck.org, Zi Yan <zi.yan@...rutgers.edu>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        linux-kselftest@...r.kernel.org, Shaohua Li <shli@...com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        "Dr . David Alan Gilbert" <dgilbert@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: [PATCH v2 2/3] userfaultfd: selftest: generalize read and poll

We do very similar things in read and poll modes, but we're copying the
codes around.  Share the codes properly on reading the message and
handling the page fault to make the code cleaner.  Meanwhile this solves
previous mismatch of behaviors between the two modes on that the old
code:

- did not check EAGAIN case in read() mode
- ignored BOUNCE_VERIFY check in read() mode

Signed-off-by: Peter Xu <peterx@...hat.com>
---
 tools/testing/selftests/vm/userfaultfd.c | 77 +++++++++++++-----------
 1 file changed, 43 insertions(+), 34 deletions(-)

diff --git a/tools/testing/selftests/vm/userfaultfd.c b/tools/testing/selftests/vm/userfaultfd.c
index 5ff3a4f9173e..7a8c6937cc67 100644
--- a/tools/testing/selftests/vm/userfaultfd.c
+++ b/tools/testing/selftests/vm/userfaultfd.c
@@ -451,6 +451,43 @@ static int copy_page(int ufd, unsigned long offset)
 	return __copy_page(ufd, offset, false);
 }
 
+static int uffd_read_msg(int ufd, struct uffd_msg *msg)
+{
+	int ret = read(uffd, msg, sizeof(*msg));
+
+	if (ret != sizeof(*msg)) {
+		if (ret < 0) {
+			if (errno == EAGAIN)
+				return 1;
+			else
+				perror("blocking read error"), exit(1);
+		} else {
+			fprintf(stderr, "short read\n"), exit(1);
+		}
+	}
+
+	return 0;
+}
+
+/* Return 1 if page fault handled by us; otherwise 0 */
+static int uffd_handle_page_fault(struct uffd_msg *msg)
+{
+	unsigned long offset;
+
+	if (msg->event != UFFD_EVENT_PAGEFAULT)
+		fprintf(stderr, "unexpected msg event %u\n",
+			msg->event), exit(1);
+
+	if (bounces & BOUNCE_VERIFY &&
+	    msg->arg.pagefault.flags & UFFD_PAGEFAULT_FLAG_WRITE)
+		fprintf(stderr, "unexpected write fault\n"), exit(1);
+
+	offset = (char *)(unsigned long)msg->arg.pagefault.address - area_dst;
+	offset &= ~(page_size-1);
+
+	return copy_page(uffd, offset);
+}
+
 static void *uffd_poll_thread(void *arg)
 {
 	unsigned long cpu = (unsigned long) arg;
@@ -458,7 +495,6 @@ static void *uffd_poll_thread(void *arg)
 	struct uffd_msg msg;
 	struct uffdio_register uffd_reg;
 	int ret;
-	unsigned long offset;
 	char tmp_chr;
 	unsigned long userfaults = 0;
 
@@ -482,25 +518,15 @@ static void *uffd_poll_thread(void *arg)
 		if (!(pollfd[0].revents & POLLIN))
 			fprintf(stderr, "pollfd[0].revents %d\n",
 				pollfd[0].revents), exit(1);
-		ret = read(uffd, &msg, sizeof(msg));
-		if (ret < 0) {
-			if (errno == EAGAIN)
-				continue;
-			perror("nonblocking read error"), exit(1);
-		}
+		if (uffd_read_msg(uffd, &msg))
+			continue;
 		switch (msg.event) {
 		default:
 			fprintf(stderr, "unexpected msg event %u\n",
 				msg.event), exit(1);
 			break;
 		case UFFD_EVENT_PAGEFAULT:
-			if (msg.arg.pagefault.flags & UFFD_PAGEFAULT_FLAG_WRITE)
-				fprintf(stderr, "unexpected write fault\n"), exit(1);
-			offset = (char *)(unsigned long)msg.arg.pagefault.address -
-				area_dst;
-			offset &= ~(page_size-1);
-			if (copy_page(uffd, offset))
-				userfaults++;
+			userfaults += uffd_handle_page_fault(&msg);
 			break;
 		case UFFD_EVENT_FORK:
 			close(uffd);
@@ -528,8 +554,6 @@ static void *uffd_read_thread(void *arg)
 {
 	unsigned long *this_cpu_userfaults;
 	struct uffd_msg msg;
-	unsigned long offset;
-	int ret;
 
 	this_cpu_userfaults = (unsigned long *) arg;
 	*this_cpu_userfaults = 0;
@@ -538,24 +562,9 @@ static void *uffd_read_thread(void *arg)
 	/* from here cancellation is ok */
 
 	for (;;) {
-		ret = read(uffd, &msg, sizeof(msg));
-		if (ret != sizeof(msg)) {
-			if (ret < 0)
-				perror("blocking read error"), exit(1);
-			else
-				fprintf(stderr, "short read\n"), exit(1);
-		}
-		if (msg.event != UFFD_EVENT_PAGEFAULT)
-			fprintf(stderr, "unexpected msg event %u\n",
-				msg.event), exit(1);
-		if (bounces & BOUNCE_VERIFY &&
-		    msg.arg.pagefault.flags & UFFD_PAGEFAULT_FLAG_WRITE)
-			fprintf(stderr, "unexpected write fault\n"), exit(1);
-		offset = (char *)(unsigned long)msg.arg.pagefault.address -
-			 area_dst;
-		offset &= ~(page_size-1);
-		if (copy_page(uffd, offset))
-			(*this_cpu_userfaults)++;
+		if (uffd_read_msg(uffd, &msg))
+			continue;
+		(*this_cpu_userfaults) += uffd_handle_page_fault(&msg);
 	}
 	return (void *)NULL;
 }
-- 
2.17.1