libfdisk: use BLKPG ioctls to inform kernel about changes

This patch introduces fdisk_reread_changes(). The function is
less invasive alternative to fdisk_reread_partition_table().

The new function uses BLKPG ioctls for modified partitions. The
another partitions are not affected. This solution allows to
successfully use fdisks on disk where some partitions are still use
(mounted). For example if you want to resize the last partition on the
device.

Signed-off-by: Karel Zak <kzak@redhat.com>

1 files changed, 102 insertions, 0 deletions

diff --git a/libfdisk/src/context.c b/libfdisk/src/context.c
index 1ebc1b981..4e359ef6a 100644
--- a/libfdisk/src/context.c
+++ b/libfdisk/src/context.c
@@ -3,6 +3,7 @@
 #endif
 
 #include "blkdev.h"
+#include "partx.h"
 #include "loopdev.h"
 #include "fdiskP.h"
 
@@ -734,6 +735,107 @@ int fdisk_reread_partition_table(struct fdisk_context *cxt)
 	return 0;
 }
 
+static inline int add_to_partitions_array(
+			struct fdisk_partition ***ary,
+			struct fdisk_partition *pa,
+			size_t *n, size_t nmax)
+{
+	if (!*ary) {
+		*ary = calloc(nmax, sizeof(struct fdisk_partition *));
+		if (!*ary)
+			return -ENOMEM;
+	}
+	(*ary)[*n] = pa;
+	(*n)++;
+	return 0;
+}
+
+/**
+ * fdisk_reread_changes:
+ * @cxt: context
+ * @org: original layout (on disk)
+ *
+ * Like fdisk_reread_partition_table() but don't forces kernel re-read all
+ * partition table. The BLKPG_* ioctls are used for individual partitions. The
+ * advantage is that unmodified partitions maybe mounted.
+ *
+ * Returns: <0 on error, or 0.
+ */
+int fdisk_reread_changes(struct fdisk_context *cxt, struct fdisk_table *org)
+{
+	struct fdisk_table *tb = NULL;
+	struct fdisk_iter itr;
+	struct fdisk_partition *pa;
+	struct fdisk_partition **rem = NULL, **add = NULL, **upd = NULL;
+	int change, rc = 0, err = 0;
+	size_t nparts, i, nadds = 0, nupds = 0, nrems = 0;
+
+	DBG(CXT, ul_debugobj(cxt, "rereading changes"));
+
+	fdisk_reset_iter(&itr, FDISK_ITER_FORWARD);
+
+	/* the current layout */
+	fdisk_get_partitions(cxt, &tb);
+	/* maximal number of partitions */
+	nparts = max(fdisk_table_get_nents(tb), fdisk_table_get_nents(org));
+
+	while (fdisk_diff_tables(org, tb, &itr, &pa, &change) == 0) {
+		if (change == FDISK_DIFF_UNCHANGED)
+			continue;
+		switch (change) {
+		case FDISK_DIFF_REMOVED:
+			rc = add_to_partitions_array(&rem, pa, &nrems, nparts);
+			break;
+		case FDISK_DIFF_ADDED:
+			rc = add_to_partitions_array(&add, pa, &nadds, nparts);
+			break;
+		case FDISK_DIFF_RESIZED:
+			rc = add_to_partitions_array(&upd, pa, &nupds, nparts);
+			break;
+		case FDISK_DIFF_MOVED:
+			rc = add_to_partitions_array(&rem, pa, &nrems, nparts);
+			rc = add_to_partitions_array(&add, pa, &nadds, nparts);
+			break;
+		}
+		if (rc != 0)
+			goto done;
+	}
+
+	for (i = 0; i < nrems; i++) {
+		pa = rem[i];
+		DBG(PART, ul_debugobj(pa, "#%zu calling BLKPG_DEL_PARTITION", pa->partno));
+		if (partx_del_partition(cxt->dev_fd, pa->partno + 1) != 0) {
+			fdisk_warn(cxt, _("Failed to remove partition %zu from system"), pa->partno + 1); 
+			err++;
+		}
+	}
+	for (i = 0; i < nupds; i++) {
+		pa = upd[i];
+		DBG(PART, ul_debugobj(pa, "#%zu calling BLKPG_RESIZE_PARTITION", pa->partno));
+		if (partx_resize_partition(cxt->dev_fd, pa->partno + 1, pa->start, pa->size) != 0) {
+			fdisk_warn(cxt, _("Failed to update system information about partition %zu"), pa->partno + 1); 
+			err++;
+		}
+	}
+	for (i = 0; i < nadds; i++) {
+		pa = add[i];
+		DBG(PART, ul_debugobj(pa, "#%zu calling BLKPG_ADD_PARTITION", pa->partno));
+		if (partx_add_partition(cxt->dev_fd, pa->partno + 1, pa->start, pa->size) != 0) {
+			fdisk_warn(cxt, _("Failed to add partition %zu to system"), pa->partno + 1); 
+			err++;
+		}
+	}
+	if (err)
+		fdisk_info(cxt,	_(
+			"The kernel still uses the old partitions. The new "
+			"table will be used at the next reboot. "));
+done:
+	free(rem);
+	free(add);
+	free(upd);
+	fdisk_unref_table(tb);
+	return rc;
+}
 
 /**
  * fdisk_device_is_used: