From b9420b8e618c8ad988c410e4289273ac962ec918 Mon Sep 17 00:00:00 2001
From: Petr Uzel <petr.uzel@suse.cz>
Date: Thu, 26 May 2016 09:28:21 +0200
Subject: [PATCH] libparted: open the device RO and lazily switch to RW only if
 necessary

Avoid useless udev events triggered by opening the device RW
for purely read-only operations.

References: https://bugzilla.novell.com/show_bug.cgi?id=979275
Author: Michael Matz <matz@suse.de>
---
 libparted/arch/linux.c | 33 ++++++++++++++++++++++++++++++---
 libparted/arch/linux.h |  1 +
 2 files changed, 31 insertions(+), 3 deletions(-)

diff --git a/libparted/arch/linux.c b/libparted/arch/linux.c
index 326b956..0a50452 100644
--- a/libparted/arch/linux.c
+++ b/libparted/arch/linux.c
@@ -294,6 +294,9 @@ static unsigned int _device_get_partition_range(PedDevice const* dev);
 static int _device_open (PedDevice* dev, int flags);
 static int _device_open_ro (PedDevice* dev);
 static int _device_close (PedDevice* dev);
+static int linux_close (PedDevice* dev);
+static void _flush_cache (PedDevice* dev);
+
 
 static int
 _read_fd (int fd, char **buf)
@@ -441,6 +444,24 @@ _is_virtblk_major (int major)
         return _major_type_in_devices (major, "virtblk");
 }
 
+static void
+_ensure_read_write (PedDevice *dev)
+{
+       PED_ASSERT (dev != NULL);
+       LinuxSpecific* arch_specific = LINUX_SPECIFIC (dev);
+
+       if (arch_specific->rw)
+              return;
+
+       if (!linux_close(dev))
+              return;
+
+       if (!_device_open (dev, RW_MODE))
+	      return;
+
+       _flush_cache (dev);
+}
+
 #ifdef ENABLE_DEVICE_MAPPER
 static int
 _dm_task_run_wait (struct dm_task *task, uint32_t cookie)
@@ -1604,6 +1625,7 @@ _flush_cache (PedDevice* dev)
 
         if (dev->read_only)
                 return;
+        _ensure_read_write (dev);
         dev->dirty = 0;
 
         ioctl (arch_specific->fd, BLKFLSBUF);
@@ -1647,7 +1669,7 @@ _device_open_ro (PedDevice* dev)
 static int
 linux_open (PedDevice* dev)
 {
-    return _device_open (dev, RW_MODE);
+    return _device_open (dev, RD_MODE);
 }
 
 static int
@@ -1685,10 +1707,12 @@ retry:
                 }
         } else {
                 dev->read_only = 0;
+		if (flags == WR_MODE || flags == RW_MODE)
+			arch_specific->rw = 1;
+		else
+			arch_specific->rw = 0;
         }
 
-        _flush_cache (dev);
-
         return 1;
 }
 
@@ -1920,6 +1944,7 @@ _write_lastoddsector (PedDevice* dev, const void* buffer)
 
         PED_ASSERT(dev != NULL);
         PED_ASSERT(buffer != NULL);
+        _ensure_read_write (dev);
 
         arch_specific = LINUX_SPECIFIC (dev);
 
@@ -1968,6 +1993,7 @@ linux_write (PedDevice* dev, const void* buffer, PedSector start,
                         return 1;
         }
 
+        _ensure_read_write (dev);
         if (_get_linux_version() < KERNEL_VERSION (2,6,0)) {
                 /* Kludge.  This is necessary to read/write the last
                    block of an odd-sized disk, until Linux 2.5.x kernel fixes.
@@ -2497,6 +2523,7 @@ _blkpg_part_command (PedDevice* dev, struct blkpg_partition* part, int op)
         LinuxSpecific*          arch_specific = LINUX_SPECIFIC (dev);
         struct blkpg_ioctl_arg  ioctl_arg;
 
+        _ensure_read_write (dev);
         ioctl_arg.op = op;
         ioctl_arg.flags = 0;
         ioctl_arg.datalen = sizeof (struct blkpg_partition);
diff --git a/libparted/arch/linux.h b/libparted/arch/linux.h
index 95def1f..926f7e2 100644
--- a/libparted/arch/linux.h
+++ b/libparted/arch/linux.h
@@ -30,6 +30,7 @@ struct _LinuxSpecific {
 	int	fd;
 	int	major;
 	int	minor;
+	int	rw;
 	char*	dmtype;         /**< device map target type */
 #if defined __s390__ || defined __s390x__
 	unsigned int real_sector_size;
-- 
1.8.4.5