[parted-devel] [PATCH 2/2] libparted: improve support for partitions on loopback devices

[Petr Uzel]

Since kernel 2.6.26, kernel allows partitions on loopback devices.
Implement support for this feature in parted.

* libparted/arch/linux.c (_sysfs_int_entry_from_dev): New function.
(_loop_get_partition_range): New function.
(_device_get_partition_range): Add special handling for loop devices.
* NEWS: Mention this change.

Signed-off-by: Petr Uzel <petr.uzel at suse.cz>
---
 NEWS                   |    4 +++
 libparted/arch/linux.c |   70 ++++++++++++++++++++++++++++++++++++++---------
 2 files changed, 60 insertions(+), 14 deletions(-)

diff --git a/NEWS b/NEWS
index cb61ac1..ed30409 100644
--- a/NEWS
+++ b/NEWS
@@ -2,6 +2,10 @@ GNU parted NEWS                                    -*- outline -*-
 
 * Noteworthy changes in release ?.? (????-??-??) [?]
 
+** New features
+
+  parted has improved support for partitionable loopback devices
+
 ** Bug fixes
 
   libparted: no longer aborts when reading a truncated GPT-formatted device
diff --git a/libparted/arch/linux.c b/libparted/arch/linux.c
index adaf89a..2c0619a 100644
--- a/libparted/arch/linux.c
+++ b/libparted/arch/linux.c
@@ -2419,32 +2419,74 @@ _blkpg_remove_partition (PedDisk* disk, int n)
                                     BLKPG_DEL_PARTITION);
 }
 
-/*
- * The number of partitions that a device can have depends on the kernel.
- * If we don't find this value in /sys/block/DEV/range, we will use our own
- * value.
- */
-static unsigned int
-_device_get_partition_range(PedDevice* dev)
+static int
+_sysfs_int_entry_from_dev(PedDevice *dev, const char *entry, int *val)
 {
-        int         range, r;
+        int         r;
         char        path[128];
         FILE*       fp;
         bool        ok;
 
-        r = snprintf(path, sizeof(path), "/sys/block/%s/range",
-                     last_component(dev->path));
+        r = snprintf(path, sizeof(path), "/sys/block/%s/%s",
+                     last_component(dev->path), entry);
         if (r < 0 || r >= sizeof(path))
-                return MAX_NUM_PARTS;
+                return 0;
 
         fp = fopen(path, "r");
         if (!fp)
-                return MAX_NUM_PARTS;
+                return 0;
 
-        ok = fscanf(fp, "%d", &range) == 1;
+        ok = fscanf(fp, "%d", val) == 1;
         fclose(fp);
 
-        /* (range <= 0) is none sense.*/
+        return ok;
+}
+
+static unsigned int
+_loop_get_partition_range(PedDevice* dev)
+{
+        int         max_part;
+        FILE*       fp;
+        bool        ok = 0;
+
+        /* max_part module param is exported since kernel 3.0 */
+        fp = fopen("/sys/module/loop/parameters/max_part", "r");
+        if (fp) {
+                ok = fscanf(fp, "%d", &max_part) == 1;
+                fclose(fp);
+        }
+
+        if (ok)
+                return max_part > 0 ? max_part : 0;
+
+        /*
+         * max_part is not exported - check ext_range;
+         * device supports partitions if ext_range > 1
+         */
+        int range;
+        ok = _sysfs_int_entry_from_dev(dev, "range", &range);
+
+        return ok && range > 1 ? range : 0;
+
+}
+
+/*
+ * The number of partitions that a device can have depends on the kernel.
+ * If we don't find this value in /sys/block/DEV/range, we will use our own
+ * value.
+ */
+static unsigned int
+_device_get_partition_range(PedDevice* dev)
+{
+        int         range;
+        bool        ok;
+
+        /* loop handling is special */
+        if (dev->type == PED_DEVICE_LOOP)
+                return _loop_get_partition_range(dev);
+
+        ok = _sysfs_int_entry_from_dev(dev, "range", &range);
+
         return ok && range > 0 ? range : MAX_NUM_PARTS;
 }
 
-- 
1.7.3.4