[gparted] Wait for udev to recreate /dev/PTN entries when calibrating (#762941)

[Curtis Gedak <gedakc src gnome org>]

commit fd9013d5f6971e9282f019903d6e148e367718bf
Author: Mike Fleetwood <mike fleetwood googlemail com>
Date:   Thu Apr 14 16:25:37 2016 +0100

    Wait for udev to recreate /dev/PTN entries when calibrating (#762941)
    
    File system specific commands sometimes fail reporting that the
    partition specific /dev entry doesn't exist.  Example failing check
    operation details:
    
        Check and repair file system (ext4) on dev/sdb4
          calibrate /dev/sdb4
            path: /dev/sdb4 (partition)
            start: 4196352
            end: 6293503
            size: 2097152 (1.00 GiB)
          check file system on /dev/sdb4 for errors and (if possible) fix them
            e2fsck -f -y -bv -C 0 /dev/sdb4
              e2fsck 1.42.9 (28-Dec-2013)
              e2fsck: No such file or directory while trying to open /dev/sdb4
              Possibly non-existent device?
    
    This has been reproduced on CentOS 7.  Debugging shows that the
    libparted calls used to re-read the partition details in
    GParted_Core::calibrate_partition() leads to udev removing and re-adding
    all the partition /dev entries for the disk.
    
        # udevadm monitor &
        # gpartedbin
        ...
         16.480662 +12.618659 calibrate_partition()          calling get_device("/dev/sdb", lp_device) ...
         16.483644 +0.002982 calibrate_partition()          get_device() returned
         16.483678 +0.000034 calibrate_partition()          calling get_disk(lp_device, lp_disk) ...
         16.618113 +0.134435 calibrate_partition()          get_disk() returned
        KERNEL[19275.707968] remove   
/devices/pci0000:00/0000:00:0d.0/ata4/host3/target3:0:0/3:0:0:0/block/sdb/sdb1 (block)
         16.618561 +0.000448 destroy_device_and_disk()      calling ped_disk_destroy(lp_disk) ...
         16.618584 +0.000023 destroy_device_and_disk()      ped_disk_destroy() returned
         16.618591 +0.000007 destroy_device_and_disk()      calling ped_device_destroy(lp_disk) ...
         16.618602 +0.000011 destroy_device_and_disk()      ped_device_destroy() returned
         16.618687 +0.000085 calibrate_partition()          return true
         16.618851 +0.000164 execute_command()              e2fsck -f -y -v -C 0 /dev/sdb4
        KERNEL[19275.708389] remove   
/devices/pci0000:00/0000:00:0d.0/ata4/host3/target3:0:0/3:0:0:0/block/sdb/sdb2 (block)
        KERNEL[19275.708500] remove   
/devices/pci0000:00/0000:00:0d.0/ata4/host3/target3:0:0/3:0:0:0/block/sdb/sdb3 (block)
        KERNEL[19275.708643] remove   
/devices/pci0000:00/0000:00:0d.0/ata4/host3/target3:0:0/3:0:0:0/block/sdb/sdb4 (block)
        KERNEL[19275.768278] change   
/devices/pci0000:00/0000:00:0d.0/ata4/host3/target3:0:0/3:0:0:0/block/sdb (block)
        KERNEL[19275.771171] add      
/devices/pci0000:00/0000:00:0d.0/ata4/host3/target3:0:0/3:0:0:0/block/sdb/sdb1 (block)
        KERNEL[19275.771360] add      
/devices/pci0000:00/0000:00:0d.0/ata4/host3/target3:0:0/3:0:0:0/block/sdb/sdb2 (block)
        KERNEL[19275.771542] add      
/devices/pci0000:00/0000:00:0d.0/ata4/host3/target3:0:0/3:0:0:0/block/sdb/sdb3 (block)
        KERNEL[19275.775858] add      
/devices/pci0000:00/0000:00:0d.0/ata4/host3/target3:0:0/3:0:0:0/block/sdb/sdb4 (block)
        UDEV  [19275.820153] remove   
/devices/pci0000:00/0000:00:0d.0/ata4/host3/target3:0:0/3:0:0:0/block/sdb/sdb3 (block)
        UDEV  [19275.823152] remove   
/devices/pci0000:00/0000:00:0d.0/ata4/host3/target3:0:0/3:0:0:0/block/sdb/sdb4 (block)
        UDEV  [19275.828275] remove   
/devices/pci0000:00/0000:00:0d.0/ata4/host3/target3:0:0/3:0:0:0/block/sdb/sdb1 (block)
         16.742735 +0.123884 execute_command()              exit status 8
        UDEV  [19275.841425] remove   
/devices/pci0000:00/0000:00:0d.0/ata4/host3/target3:0:0/3:0:0:0/block/sdb/sdb2 (block)
        UDEV  [19275.905478] change   
/devices/pci0000:00/0000:00:0d.0/ata4/host3/target3:0:0/3:0:0:0/block/sdb (block)
        UDEV  [19276.013580] add      
/devices/pci0000:00/0000:00:0d.0/ata4/host3/target3:0:0/3:0:0:0/block/sdb/sdb3 (block)
        UDEV  [19276.034728] add      
/devices/pci0000:00/0000:00:0d.0/ata4/host3/target3:0:0/3:0:0:0/block/sdb/sdb4 (block)
        UDEV  [19276.174840] add      
/devices/pci0000:00/0000:00:0d.0/ata4/host3/target3:0:0/3:0:0:0/block/sdb/sdb1 (block)
        UDEV  [19276.237105] add      
/devices/pci0000:00/0000:00:0d.0/ata4/host3/target3:0:0/3:0:0:0/block/sdb/sdb2 (block)
    
    So exactly when GParted is running the external e2fsck command, udev is
    in the middle of removing and re-adding all the /dev partition entries
    for the disk.  Hence the above failure reporting that /dev/sdb4 didn't
    exist.  This error depends on the timing between GParted running the
    external file system specific command and udev removing and re-adding
    the entries, so sometimes it works and sometimes it fails.
    
    Further debugging showed that simply opening and closing the whole disk
    device read-write triggers the same removing and re-adding of all the
    partition /dev entries with udev >= 219.  Opening the whole disk device
    read-write is what libparted has always done until this post
    libparted 3.2 patch to make it open read-only when probing:
    
        http://git.savannah.gnu.org/cgit/parted.git/commit/?id=44d5ae0115c4ecfe3158748309e9912c5aede92d
        libparted: Use read only when probing devices on linux (#1245144)
    
    To fix this simply wait for udev devices to settle in
    calibrate_partitions().  The longest I have seen udev take to do this is
    0.80 seconds in a VM.  Wait up to 10 seconds as is done in commit() ->
    commit_to_os(), also called when applying operations.
    
    On configurations which don't have this issue execution of udevadm
    settle, which will return immediately, adds at most 0.1 seconds to the
    time taken for the calibrate step.  This won't be noticed in the time
    taken of the operation details so there is no point in trying to avoid
    executing udevadm settle when not needed.
    
    Bug 762941 - Operations sometimes failing with: No such file or
                 directory

 src/GParted_Core.cc |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)
---
diff --git a/src/GParted_Core.cc b/src/GParted_Core.cc
index be6665c..2abc7df 100644
--- a/src/GParted_Core.cc
+++ b/src/GParted_Core.cc
@@ -3521,6 +3521,12 @@ bool GParted_Core::calibrate_partition( Partition & partition, OperationDetail &
                        destroy_device_and_disk( lp_device, lp_disk ) ;
                }
 
+               // (#762941) Above libparted partition querying triggers udev >= 219 to
+               // remove and re-add all the partition specific /dev/ entries.  Wait for
+               // this to complete to avoid FS specific commands failing because they
+               // happen to run just when the needed /dev/PTN entry doesn't exist.
+               settle_device( 10 );
+
                operationdetail.get_last_child().set_status( success ? STATUS_SUCCES : STATUS_ERROR );
                return success;
        }