libfdisk: add fdisk_save_user_grain()

Let's provide API for applications that don't want to use the default
1MiB grain. The new function allow to use "as minimal as possible" if
grain is set by fdisk_save_user_grain() to 512.

If the phy sector size (or minimal I/O size) is greater than specified
grain size than smallest possible setting is used.

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

5 files changed, 46 insertions, 1 deletions

diff --git a/libfdisk/docs/libfdisk-sections.txt b/libfdisk/docs/libfdisk-sections.txt
index 68ca0927f..37ceffa86 100644
--- a/libfdisk/docs/libfdisk-sections.txt
+++ b/libfdisk/docs/libfdisk-sections.txt
@@ -69,6 +69,7 @@ fdisk_override_geometry
 fdisk_reset_alignment
 fdisk_reset_device_properties
 fdisk_save_user_geometry
+fdisk_save_user_grain
 fdisk_save_user_sector_size
 </SECTION>
 
diff --git a/libfdisk/src/alignment.c b/libfdisk/src/alignment.c
index 6b395b48c..4c9fbcb9a 100644
--- a/libfdisk/src/alignment.c
+++ b/libfdisk/src/alignment.c
@@ -26,7 +26,7 @@
  * It's recommended to not change any alignment or device properties. All is
  * initialized by default by fdisk_assign_device().
  *
- * Note that terminology used by libfdisk is: 
+ * Note that terminology used by libfdisk is:
  *   - device properties: I/O limits (topology), geometry, sector size, ...
  *   - alignment: first, last LBA, grain, ...
  *
@@ -314,6 +314,36 @@ int fdisk_save_user_sector_size(struct fdisk_context *cxt,
 }
 
 /**
+ * fdisk_save_user_grain:
+ * @cxt: context
+ * @grain: size in bytes (>= 512, multiple of 512)
+ *
+ * Save user define grain size. The size is used to align partitions.
+ *
+ * The default is 1MiB (or optimal I/O size if greater than 1MiB). It's strongly
+ * recommended to use the default.
+ *
+ * The smallest possible granularity for partitioning is physical sector size
+ * (or minimal I/O size; the bigger number win). If the user's @grain size is
+ * too small than the smallest possible granularity is used. It means
+ * fdisk_save_user_grain(cxt, 512) forces libfdisk to use grain as small as
+ * possible.
+ *
+ * The setting is applied by fdisk_assign_device() or
+ * fdisk_reset_device_properties().
+ *
+ * Returns: <0 on error, 0 on success.
+ */
+int fdisk_save_user_grain(struct fdisk_context *cxt, unsigned long grain)
+{
+	if (!cxt || grain % 512)
+		return -EINVAL;
+
+	cxt->user_grain = grain;
+	return 0;
+}
+
+/**
  * fdisk_has_user_device_properties:
  * @cxt: context
  *
@@ -322,6 +352,7 @@ int fdisk_save_user_sector_size(struct fdisk_context *cxt,
 int fdisk_has_user_device_properties(struct fdisk_context *cxt)
 {
 	return (cxt->user_pyh_sector || cxt->user_log_sector ||
+		cxt->user_grain ||
 		fdisk_has_user_device_geometry(cxt));
 }
 
@@ -363,6 +394,14 @@ int fdisk_apply_user_device_properties(struct fdisk_context *cxt)
 		recount_geometry(cxt);
 
 	fdisk_reset_alignment(cxt);
+
+	if (cxt->user_grain) {
+		unsigned long granularity = max(cxt->phy_sector_size, cxt->min_io_size);
+
+		cxt->grain = cxt->user_grain < granularity ? granularity : cxt->user_grain;
+		DBG(CXT, ul_debugobj(cxt, "new grain: %lu", cxt->grain));
+	}
+
 	if (cxt->firstsector_bufsz != cxt->sector_size)
 		fdisk_read_firstsector(cxt);
 
diff --git a/libfdisk/src/fdiskP.h b/libfdisk/src/fdiskP.h
index 1796e18e1..23903b4b4 100644
--- a/libfdisk/src/fdiskP.h
+++ b/libfdisk/src/fdiskP.h
@@ -399,6 +399,7 @@ struct fdisk_context {
 	struct fdisk_geometry user_geom;
 	unsigned long user_pyh_sector;
 	unsigned long user_log_sector;
+	unsigned long user_grain;
 
 	struct fdisk_label *label;	/* current label, pointer to labels[] */
 
diff --git a/libfdisk/src/libfdisk.h.in b/libfdisk/src/libfdisk.h.in
index 1c16fe4b3..3586d6626 100644
--- a/libfdisk/src/libfdisk.h.in
+++ b/libfdisk/src/libfdisk.h.in
@@ -503,6 +503,9 @@ int fdisk_save_user_geometry(struct fdisk_context *cxt,
 int fdisk_save_user_sector_size(struct fdisk_context *cxt,
 				unsigned int phy,
 				unsigned int log);
+
+int fdisk_save_user_grain(struct fdisk_context *cxt, unsigned long grain);
+
 int fdisk_has_user_device_properties(struct fdisk_context *cxt);
 int fdisk_reset_alignment(struct fdisk_context *cxt);
 int fdisk_reset_device_properties(struct fdisk_context *cxt);
diff --git a/libfdisk/src/libfdisk.sym b/libfdisk/src/libfdisk.sym
index 0d274847a..2c892a0c3 100644
--- a/libfdisk/src/libfdisk.sym
+++ b/libfdisk/src/libfdisk.sym
@@ -289,4 +289,5 @@ FDISK_2.31 {
 	fdisk_reread_changes;
 	fdisk_disable_dialogs;
 	fdisk_has_dialogs;
+	fdisk_save_user_grain;
 } FDISK_2.30;