blktap2: Fix naked unchecked uses of read/write/chdir.

These cause warnings under warn_unused_result, and for read/write we
ought to deal with partial io results.

Signed-off-by: Keir Fraser <keir@xen.org>

7 files changed, 56 insertions, 8 deletions

diff --git a/tools/blktap2/drivers/tapdisk-diff.c b/tools/blktap2/drivers/tapdisk-diff.c
index 1d2ba8e682..056d4c9f60 100644
--- a/tools/blktap2/drivers/tapdisk-diff.c
+++ b/tools/blktap2/drivers/tapdisk-diff.c
@@ -39,6 +39,7 @@
 #include "tapdisk-vbd.h"
 #include "tapdisk-server.h"
 #include "tapdisk-disktype.h"
+#include "tapdisk-utils.h"
 #include "libvhd.h"
 
 #define POLL_READ                        0
@@ -170,7 +171,7 @@ tapdisk_stream_poll_clear(struct tapdisk_stream_poll *p)
 {
 	int dummy;
 
-	read(p->pipe[POLL_READ], &dummy, sizeof(dummy));
+	read_exact(p->pipe[POLL_READ], &dummy, sizeof(dummy));
 	p->set = 0;
 }
 
@@ -180,7 +181,7 @@ tapdisk_stream_poll_set(struct tapdisk_stream_poll *p)
 	int dummy = 0;
 
 	if (!p->set) {
-		write(p->pipe[POLL_WRITE], &dummy, sizeof(dummy));
+		write_exact(p->pipe[POLL_WRITE], &dummy, sizeof(dummy));
 		p->set = 1;
 	}
 }
diff --git a/tools/blktap2/drivers/tapdisk-log.c b/tools/blktap2/drivers/tapdisk-log.c
index 1220bf927e..d14da32415 100644
--- a/tools/blktap2/drivers/tapdisk-log.c
+++ b/tools/blktap2/drivers/tapdisk-log.c
@@ -37,6 +37,7 @@
 #include <sys/time.h>
 
 #include "tapdisk-log.h"
+#include "tapdisk-utils.h"
 
 #define MAX_ENTRY_LEN      512
 #define MAX_ERROR_MESSAGES 16
@@ -247,7 +248,7 @@ tlog_flush(void)
 	wsize = ((size + 511) & (~511));
 
 	memset(tapdisk_log.buf + size, '\n', wsize - size);
-	write(fd, tapdisk_log.buf, wsize);
+	write_exact(fd, tapdisk_log.buf, wsize);
 
 	tapdisk_log.p = tapdisk_log.buf;
 
diff --git a/tools/blktap2/drivers/tapdisk-queue.c b/tools/blktap2/drivers/tapdisk-queue.c
index b6394bfdad..1a9403828b 100644
--- a/tools/blktap2/drivers/tapdisk-queue.c
+++ b/tools/blktap2/drivers/tapdisk-queue.c
@@ -435,7 +435,7 @@ tapdisk_lio_ack_event(struct tqueue *queue)
 	uint64_t val;
 
 	if (lio->flags & LIO_FLAG_EVENTFD)
-		read(lio->event_fd, &val, sizeof(val));
+		read_exact(lio->event_fd, &val, sizeof(val));
 }
 
 static void
diff --git a/tools/blktap2/drivers/tapdisk-stream.c b/tools/blktap2/drivers/tapdisk-stream.c
index 1795abddfd..b5b0fa7869 100644
--- a/tools/blktap2/drivers/tapdisk-stream.c
+++ b/tools/blktap2/drivers/tapdisk-stream.c
@@ -38,6 +38,7 @@
 #include "tapdisk-vbd.h"
 #include "tapdisk-server.h"
 #include "tapdisk-disktype.h"
+#include "tapdisk-utils.h"
 
 #define POLL_READ                        0
 #define POLL_WRITE                       1
@@ -145,7 +146,7 @@ tapdisk_stream_poll_clear(struct tapdisk_stream_poll *p)
 {
 	int dummy;
 
-	read(p->pipe[POLL_READ], &dummy, sizeof(dummy));
+	read_exact(p->pipe[POLL_READ], &dummy, sizeof(dummy));
 	p->set = 0;
 }
 
@@ -155,7 +156,7 @@ tapdisk_stream_poll_set(struct tapdisk_stream_poll *p)
 	int dummy = 0;
 
 	if (!p->set) {
-		write(p->pipe[POLL_WRITE], &dummy, sizeof(dummy));
+		write_exact(p->pipe[POLL_WRITE], &dummy, sizeof(dummy));
 		p->set = 1;
 	}
 }
@@ -203,7 +204,7 @@ tapdisk_stream_print_request(struct tapdisk_stream *s,
 {
 	unsigned long idx = (unsigned long)tapdisk_stream_request_idx(s, sreq);
 	char *buf = (char *)MMAP_VADDR(s->vbd->ring.vstart, idx, 0);
-	write(s->out_fd, buf, sreq->secs << SECTOR_SHIFT);
+	write_exact(s->out_fd, buf, sreq->secs << SECTOR_SHIFT);
 }
 
 static void
diff --git a/tools/blktap2/drivers/tapdisk-utils.c b/tools/blktap2/drivers/tapdisk-utils.c
index 1b15f12154..44840efbf8 100644
--- a/tools/blktap2/drivers/tapdisk-utils.c
+++ b/tools/blktap2/drivers/tapdisk-utils.c
@@ -175,3 +175,40 @@ int tapdisk_linux_version(void)
 }
 
 #endif
+int read_exact(int fd, void *data, size_t size)
+{
+    size_t offset = 0;
+    ssize_t len;
+
+    while ( offset < size )
+    {
+        len = read(fd, (char *)data + offset, size - offset);
+        if ( (len == -1) && (errno == EINTR) )
+            continue;
+        if ( len == 0 )
+            errno = 0;
+        if ( len <= 0 )
+            return -1;
+        offset += len;
+    }
+
+    return 0;
+}
+
+int write_exact(int fd, const void *data, size_t size)
+{
+    size_t offset = 0;
+    ssize_t len;
+
+    while ( offset < size )
+    {
+        len = write(fd, (const char *)data + offset, size - offset);
+        if ( (len == -1) && (errno == EINTR) )
+            continue;
+        if ( len <= 0 )
+            return -1;
+        offset += len;
+    }
+
+    return 0;
+}
diff --git a/tools/blktap2/drivers/tapdisk-utils.h b/tools/blktap2/drivers/tapdisk-utils.h
index 7b7c3d5e92..aced8ef492 100644
--- a/tools/blktap2/drivers/tapdisk-utils.h
+++ b/tools/blktap2/drivers/tapdisk-utils.h
@@ -39,4 +39,7 @@ int tapdisk_namedup(char **, const char *);
 int tapdisk_get_image_size(int, uint64_t *, uint32_t *);
 int tapdisk_linux_version(void);
 
+int read_exact(int fd, void *data, size_t size); /* EOF => -1, errno=0 */
+int write_exact(int fd, const void *data, size_t size);
+
 #endif
diff --git a/tools/blktap2/drivers/tapdisk2.c b/tools/blktap2/drivers/tapdisk2.c
index dae0b81efe..aebd861aa5 100644
--- a/tools/blktap2/drivers/tapdisk2.c
+++ b/tools/blktap2/drivers/tapdisk2.c
@@ -79,7 +79,12 @@ main(int argc, char *argv[])
 	if (optind != argc)
 		usage(argv[0], EINVAL);
 
-	chdir("/");
+	if (chdir("/")) {
+		DPRINTF("failed to chdir(/): %d\n", errno);
+		err = 1;
+		goto out;
+	}
+
 	tapdisk_start_logging("tapdisk2");
 
 	err = tapdisk_server_init();