Regular file support for loopback + test

Makefile

@@ -25,6 +25,7 @@ $(LIBOBJS): %.o: %.c
 test: $(TARGET)
 	PATH=$(PWD):$$PATH sudo test/busexmp.sh
 	PATH=$(PWD):$$PATH sudo test/signal_termination.sh
+	PATH=$(PWD):$$PATH sudo test/loopback_device.sh
 
 clean:
 	rm -f $(TARGET) $(OBJS) $(STATIC_LIB)

loopback.c

@@ -21,10 +21,11 @@
 #define _LARGEFILE64_SOURCE
 
 #include <assert.h>
+#include <err.h>
 #include <fcntl.h>
 #include <stdio.h>
+#include <stdlib.h>
 #include <sys/mount.h>
-#include <sys/types.h>
 #include <sys/stat.h>
 #include <unistd.h>
 
@@ -34,7 +35,10 @@ static int fd;
 
 static void usage(void)
 {
-    fprintf(stderr, "Usage: loopback <phyical device> <virtual device>\n");
+    fprintf(stderr,
+        "Usage: loopback <phyical device or file> <virtual device>\n"
+        "  for example: loopback path/to/file /dev/nbd0\n"
+    );
 }
 
 static int loopback_read(void *buf, u_int32_t len, u_int64_t offset, void *userdata)
@@ -77,7 +81,6 @@ static struct buse_operations bop = {
 int main(int argc, char *argv[])
 {
     struct stat buf;
-    int err;
     int64_t size;
 
     if (argc != 3) {
@@ -88,16 +91,17 @@ int main(int argc, char *argv[])
     fd = open(argv[1], O_RDWR|O_LARGEFILE);
     assert(fd != -1);
 
-    /* Let's verify that this file is actually a block device. We could support
-     * regular files, too, but we don't need to right now. */
-    fstat(fd, &buf);
-    assert(S_ISBLK(buf.st_mode));
+    /* Figure out the size of the file or underlying block device. */
+    if (fstat(fd, &buf) != 0) err(EXIT_FAILURE, NULL);
+    if (S_ISBLK(buf.st_mode)) {
+        /* it's a block dev */
+        if(ioctl(fd, BLKGETSIZE64, &size) != 0) err(EXIT_FAILURE, NULL);
+    } else {
+        /* a file */
+        size = buf.st_size;
+    }
 
-    /* Figure out the size of the underlying block device. */
-    err = ioctl(fd, BLKGETSIZE64, &size);
-    assert(err != -1);
-    (void)err;
-    fprintf(stderr, "The size of this device is %ld bytes.\n", size);
+    fprintf(stderr, "The size of this device/file is %ld bytes.\n", size);
     bop.size = size;
 
     buse_main(argv[2], &bop, NULL);

test/busexmp.sh

@@ -1,23 +1,17 @@
 #!/usr/bin/env bash
 set -e
+source ./test/utils.sh
 
 BLOCKDEV=/dev/nbd0
 # quiet version of dd
 DD="dd status=none"
 
-# verify if blockdev is not currently in use
-set +e
-nbd-client -c "$BLOCKDEV" > /dev/null
-if [ $? -ne 1 ]; then
-	echo "device $BLOCKDEV is not ready to use (already in use or corrupted)"
-	exit 1
-fi
-set -e
+ensure_buse_device_free "$BLOCKDEV"
 
 # on exit do cleanup actions
 function cleanup () {
-	# kill and wait for BUSE background job
-	nbd-client -d "$BLOCKDEV" > /dev/null
+	# disconnect and wait for BUSE background job
+	disconnect_buse_device "$BLOCKDEV"
 	wait $BUSEPID
 	# remove the test file
 	rm -f "$TESTFILE"

test/loopback_device.sh

@@ -0,0 +1,54 @@
+#!/usr/bin/env bash
+set -e
+source ./test/utils.sh
+
+BLOCKDEV=/dev/nbd0
+FAKE_BLOCK_DEVICE=/dev/fake-dev0
+# quiet version of dd
+DD="dd status=none"
+
+ensure_buse_device_free "$BLOCKDEV"
+
+# ensure FAKE_BLOCK_DEVICE is not in use
+set +e
+losetup "$FAKE_BLOCK_DEVICE" 2> /dev/null
+if [ $? -ne 1 ]; then
+	echo "device $FAKE_BLOCK_DEVICE is not ready to use (already in use or corrupted)"
+	exit 1
+fi
+set -e
+
+# on exit do cleanup actions
+function cleanup () {
+	# kill and wait for BUSE background job
+	disconnect_buse_device "$BLOCKDEV"
+	wait $BUSEPID
+	# remove fake block device
+	losetup -d "$FAKE_BLOCK_DEVICE"
+	rm -f "$FAKE_BLOCK_DEVICE"
+	# remove the test file
+	rm -f "$TESTFILE"
+}
+trap cleanup EXIT
+
+# prepare fake block device
+TESTFILE=$(mktemp)
+$DD if=/dev/urandom of="$TESTFILE" bs=16M count=1
+mknod "$FAKE_BLOCK_DEVICE" b 7 200 
+losetup "$FAKE_BLOCK_DEVICE" "$TESTFILE"
+
+# attach BUSE device
+loopback "$FAKE_BLOCK_DEVICE" "$BLOCKDEV" &
+sleep 1
+BUSEPID=$!
+
+### do checks ###
+
+# compare data read from nbd with TESTFILE contents
+cmp <($DD if="$BLOCKDEV" ibs=1k count=5 skip=54) <($DD if="$TESTFILE" ibs=1k count=5 skip=54)
+
+# write data at the end
+$DD if="$TESTFILE" of="$BLOCKDEV" bs=1M count=2 seek=14
+
+# read extending past the end of device
+cmp <($DD if="$BLOCKDEV" bs=1M count=5 skip=14) <($DD if="$TESTFILE" bs=1M count=2)

test/signal_termination.sh

@@ -1,21 +1,15 @@
 #!/usr/bin/env bash
 set -e
+source ./test/utils.sh
 
 BLOCKDEV=/dev/nbd0
 SIZE=16M
 
-# verify if blockdev is not currently in use
-set +e
-nbd-client -c "$BLOCKDEV" > /dev/null
-if [ $? -ne 1 ]; then
-	echo "device $BLOCKDEV is not ready to use (already in use or corrupted)"
-	exit 1
-fi
-set -e
+ensure_buse_device_free "$BLOCKDEV"
 
 # on exit make sure nbd is disconnected
 function cleanup () {
-	nbd-client -d "$BLOCKDEV" > /dev/null
+	disconnect_buse_device "$BLOCKDEV"
 }
 trap cleanup EXIT
 

test/utils.sh

@@ -0,0 +1,14 @@
+function ensure_buse_device_free () {
+	# verify if blockdev is not currently in use
+	set +e
+	nbd-client -c "$1" > /dev/null
+	if [ $? -ne 1 ]; then
+		echo "device $1 is not ready to use (already in use or corrupted)"
+		exit 1
+	fi
+	set -e
+}
+
+function disconnect_buse_device () {
+	nbd-client -d "$1" > /dev/null
+}