libfdisk: add fdisk_assign_device_by_fd()

It's possible that caller has the device already opened for some
other task, so let's reuse the file descriptor.

Requested-by: Lennart Poettering <lennart@poettering.net>
Signed-off-by: Karel Zak <kzak@redhat.com>

5 files changed, 99 insertions, 48 deletions

diff --git a/libfdisk/docs/libfdisk-sections.txt b/libfdisk/docs/libfdisk-sections.txt
index d0d362f60..f148da527 100644
--- a/libfdisk/docs/libfdisk-sections.txt
+++ b/libfdisk/docs/libfdisk-sections.txt
@@ -291,6 +291,7 @@ fdisk_unref_table
 <FILE>context</FILE>
 fdisk_context
 fdisk_assign_device
+fdisk_assign_device_by_fd
 fdisk_deassign_device
 fdisk_reassign_device
 fdisk_device_is_used
diff --git a/libfdisk/src/context.c b/libfdisk/src/context.c
index 1171f28a8..b62d2b101 100644
--- a/libfdisk/src/context.c
+++ b/libfdisk/src/context.c
@@ -541,7 +541,7 @@ static void reset_context(struct fdisk_context *cxt)
 			free(cxt->firstsector);
 	} else {
 		/* we close device only in primary context */
-		if (cxt->dev_fd > -1)
+		if (cxt->dev_fd > -1 && cxt->private_fd)
 			close(cxt->dev_fd);
 		free(cxt->firstsector);
 	}
@@ -559,6 +559,7 @@ static void reset_context(struct fdisk_context *cxt)
 	memset(&cxt->dev_st, 0, sizeof(cxt->dev_st));
 
 	cxt->dev_fd = -1;
+	cxt->private_fd = 0;
 	cxt->firstsector = NULL;
 	cxt->firstsector_bufsz = 0;
 
@@ -572,39 +573,12 @@ static void reset_context(struct fdisk_context *cxt)
 	fdisk_free_wipe_areas(cxt);
 }
 
-/**
- * fdisk_assign_device:
- * @cxt: context
- * @fname: path to the device to be handled
- * @readonly: how to open the device
- *
- * Open the device, discovery topology, geometry, detect disklabel, check for
- * collisions and switch the current label driver to reflect the probing
- * result.
- *
- * If in standard mode (!= non-listonly mode) than also detects for collisions.
- * The result is accessible by fdisk_get_collision() and
- * fdisk_is_ptcollision().  The collision (e.g. old obsolete PT) may be removed
- * by fdisk_enable_wipe().  Note that new PT and old PT may be on different
- * locations.
- *
- * Note that this function resets all generic setting in context.
- *
- * If the @cxt is nested context (necessary for example to edit BSD or PMBR)
- * then the device is assigned to the parental context and necessary properties
- * are copied to the @cxt. The change is propagated in child->parent direction
- * only. It's impossible to use a different device for primary and nested
- * contexts.
- *
- * Returns: 0 on success, < 0 on error.
- */
-int fdisk_assign_device(struct fdisk_context *cxt,
-			const char *fname, int readonly)
+/* fdisk_assign_device() body */
+static int fdisk_assign_fd(struct fdisk_context *cxt, int fd,
+			const char *fname, int readonly, int privfd)
 {
-	int fd;
-
-	DBG(CXT, ul_debugobj(cxt, "assigning device %s", fname));
 	assert(cxt);
+	assert(fd >= 0);
 
 	/* redirect request to parent */
 	if (cxt->parent) {
@@ -615,7 +589,7 @@ int fdisk_assign_device(struct fdisk_context *cxt,
 		 * unwanted extra warnings. */
 		fdisk_enable_listonly(cxt->parent, fdisk_is_listonly(cxt));
 
-		rc = fdisk_assign_device(cxt->parent, fname, readonly);
+		rc = fdisk_assign_fd(cxt->parent, fd, fname, readonly, privfd);
 		fdisk_enable_listonly(cxt->parent, org);
 
 		if (!rc)
@@ -627,16 +601,13 @@ int fdisk_assign_device(struct fdisk_context *cxt,
 
 	reset_context(cxt);
 
-	fd = open(fname, (readonly ? O_RDONLY : O_RDWR ) | O_CLOEXEC);
-	if (fd < 0)
-		goto fail;
-
 	if (fstat(fd, &cxt->dev_st) != 0)
 		goto fail;
 
 	cxt->readonly = readonly;
 	cxt->dev_fd = fd;
-	cxt->dev_path = strdup(fname);
+	cxt->private_fd = privfd;
+	cxt->dev_path = fname ? strdup(fname) : NULL;
 	if (!cxt->dev_path)
 		goto fail;
 
@@ -649,7 +620,6 @@ int fdisk_assign_device(struct fdisk_context *cxt,
 		goto fail;
 
 	fdisk_probe_labels(cxt);
-
 	fdisk_apply_label_device_properties(cxt);
 
 	/* warn about obsolete stuff on the device if we aren't in
@@ -664,14 +634,79 @@ int fdisk_assign_device(struct fdisk_context *cxt,
 fail:
 	{
 		int rc = -errno;
-		if (fd >= 0)
-			close(fd);
 		DBG(CXT, ul_debugobj(cxt, "failed to assign device [rc=%d]", rc));
 		return rc;
 	}
 }
 
 /**
+ * fdisk_assign_device:
+ * @cxt: context
+ * @fname: path to the device to be handled
+ * @readonly: how to open the device
+ *
+ * Open the device, discovery topology, geometry, detect disklabel, check for
+ * collisions and switch the current label driver to reflect the probing
+ * result.
+ *
+ * If in standard mode (!= non-listonly mode) than also detects for collisions.
+ * The result is accessible by fdisk_get_collision() and
+ * fdisk_is_ptcollision().  The collision (e.g. old obsolete PT) may be removed
+ * by fdisk_enable_wipe().  Note that new PT and old PT may be on different
+ * locations.
+ *
+ * Note that this function resets all generic setting in context.
+ *
+ * If the @cxt is nested context (necessary for example to edit BSD or PMBR)
+ * then the device is assigned to the parental context and necessary properties
+ * are copied to the @cxt. The change is propagated in child->parent direction
+ * only. It's impossible to use a different device for primary and nested
+ * contexts.
+ *
+ * Returns: 0 on success, < 0 on error.
+ */
+int fdisk_assign_device(struct fdisk_context *cxt,
+			const char *fname, int readonly)
+{
+	int fd, rc;
+
+	DBG(CXT, ul_debugobj(cxt, "assigning device %s", fname));
+	assert(cxt);
+
+	fd = open(fname, (readonly ? O_RDONLY : O_RDWR ) | O_CLOEXEC);
+	if (fd < 0) {
+		int rc = -errno;
+		DBG(CXT, ul_debugobj(cxt, "failed to assign device [rc=%d]", rc));
+		return rc;
+	}
+
+	rc = fdisk_assign_fd(cxt, fd, fname, readonly, 1);
+	if (rc)
+		close(fd);
+	return rc;
+}
+
+/**
+ * fdisk_assign_device_by_fd:
+ * @cxt: context
+ * @fd: device file descriptor
+ * @fname: path to the device (used for dialogs, debugging, partition names, ...)
+ * @readonly: how to use the device
+ *
+ * Like fdisk_assign_device(), but caller is responsible to open and close the
+ * device. The library only fsync() the device on fdisk_deassign_device().
+ *
+ * The device has to be open O_RDWR on @readonly=0.
+ *
+ * Returns: 0 on success, < 0 on error.
+ */
+int fdisk_assign_device_by_fd(struct fdisk_context *cxt, int fd,
+			const char *fname, int readonly)
+{
+	return fdisk_assign_fd(cxt, fd, fname, readonly, 0);
+}
+
+/**
  * fdisk_deassign_device:
  * @cxt: context
  * @nosync: disable fsync()
@@ -696,15 +731,19 @@ int fdisk_deassign_device(struct fdisk_context *cxt, int nosync)
 
 	DBG(CXT, ul_debugobj(cxt, "de-assigning device %s", cxt->dev_path));
 
-	if (cxt->readonly)
+	if (cxt->readonly && cxt->private_fd)
 		close(cxt->dev_fd);
 	else {
-		if (fsync(cxt->dev_fd) || close(cxt->dev_fd)) {
+		if (fsync(cxt->dev_fd)) {
+			fdisk_warn(cxt, _("%s: fsync device failed"),
+					cxt->dev_path);
+			return -errno;
+		}
+		if (cxt->private_fd && close(cxt->dev_fd)) {
 			fdisk_warn(cxt, _("%s: close device failed"),
 					cxt->dev_path);
 			return -errno;
 		}
-
 		if (!nosync) {
 			fdisk_info(cxt, _("Syncing disks."));
 			sync();
@@ -713,7 +752,6 @@ int fdisk_deassign_device(struct fdisk_context *cxt, int nosync)
 
 	free(cxt->dev_path);
 	cxt->dev_path = NULL;
-
 	cxt->dev_fd = -1;
 
 	return 0;
@@ -733,7 +771,7 @@ int fdisk_deassign_device(struct fdisk_context *cxt, int nosync)
 int fdisk_reassign_device(struct fdisk_context *cxt)
 {
 	char *devname;
-	int rdonly, rc;
+	int rdonly, rc, fd, privfd;
 
 	assert(cxt);
 	assert(cxt->dev_fd >= 0);
@@ -745,11 +783,19 @@ int fdisk_reassign_device(struct fdisk_context *cxt)
 		return -ENOMEM;
 
 	rdonly = cxt->readonly;
+	fd = cxt->dev_fd;
+	privfd = cxt->private_fd;
 
 	fdisk_deassign_device(cxt, 1);
-	rc = fdisk_assign_device(cxt, devname, rdonly);
-	free(devname);
 
+	if (privfd)
+		/* reopen and assign */
+		rc = fdisk_assign_device(cxt, devname, rdonly);
+	else
+		/* assign only */
+		rc = fdisk_assign_fd(cxt, fd, devname, rdonly, privfd);
+
+	free(devname);
 	return rc;
 }
 
diff --git a/libfdisk/src/fdiskP.h b/libfdisk/src/fdiskP.h
index 19c1c7953..fefebae2a 100644
--- a/libfdisk/src/fdiskP.h
+++ b/libfdisk/src/fdiskP.h
@@ -389,6 +389,7 @@ struct fdisk_context {
 		     pt_collision : 1,		/* another PT detected by libblkid */
 		     no_disalogs : 1,		/* disable dialog-driven partititoning */
 		     dev_model_probed : 1,	/* tried to read from sys */
+		     private_fd : 1,		/* open by libfdisk */
 		     listonly : 1;		/* list partition, nothing else */
 
 	char *collision;			/* name of already existing FS/PT */
diff --git a/libfdisk/src/libfdisk.h.in b/libfdisk/src/libfdisk.h.in
index 69c6fd820..0669c0a7c 100644
--- a/libfdisk/src/libfdisk.h.in
+++ b/libfdisk/src/libfdisk.h.in
@@ -195,6 +195,8 @@ int fdisk_is_labeltype(struct fdisk_context *cxt, enum fdisk_labeltype id);
 
 int fdisk_assign_device(struct fdisk_context *cxt,
 			const char *fname, int readonly);
+int fdisk_assign_device_by_fd(struct fdisk_context *cxt, int fd,
+                        const char *fname, int readonly);
 int fdisk_deassign_device(struct fdisk_context *cxt, int nosync);
 int fdisk_reassign_device(struct fdisk_context *cxt);
 
diff --git a/libfdisk/src/libfdisk.sym b/libfdisk/src/libfdisk.sym
index 8ce943acc..96fcadd71 100644
--- a/libfdisk/src/libfdisk.sym
+++ b/libfdisk/src/libfdisk.sym
@@ -306,4 +306,5 @@ FDISK_2.33 {
 
 FDISK_2.35 {
 	fdisk_script_set_table;
+	fdisk_assign_device_by_fd;
 } FDISK_2.33;