No change notification for o.fd.UDisks2.Filesystem.Size anymore

[mvollmer]

I think we lost the property change notifications with #949, no?

[tbzatek]

Ah right, it was changed to be on demand only. I knew why I wasn't convinced to push this change to stable...

Hmm, hmm, the problem was an endless uevent storm so we had to decouple that. Caused by certain filesystems that generate extra uevent once you retrieve the filesystem size. And we simply can't refresh the fs size as a result of a uvent, no matter how delayed the refresh would be. The change to the behaviour was a compromise between changing the API, deprecation and introducing a getter method.

If it's suitable for your use case, can you just use the built-in org.freedesktop.DBus.Properties.Get() method to trigger the refresh after you make any modification to the filesystem or on a first object retrieval? I suppose this value wouldn't change often.

[mvollmer]

I think we really should fix dumpe2fs or stop using it. Here is a potential fix: tytso/e2fsprogs#122

To stop using it, libblockdev could use libext2fs directly instead of spawning dumpe2fs. That's probably a good idea in general. I'll have a stab at that.

[mvollmer]

Here is my first toy program, looks promising:

#include <stdio.h>
#include <ext2fs.h>

void
main (int argc, char **argv)
{
  errcode_t retval;
  ext2_filsys fs;

  retval = ext2fs_open (argv[1],
                        EXT2_FLAG_JOURNAL_DEV_OK | EXT2_FLAG_SOFTSUPP_FEATURES |
                        EXT2_FLAG_64BITS | EXT2_FLAG_THREADS | EXT2_FLAG_SUPER_ONLY |
                        EXT2_FLAG_IGNORE_CSUM_ERRORS,
                        0, // use_superblock
                        0, // use_blocksize
                        unix_io_manager,
                        &fs);

  if (retval) {
    printf ("OPEN %d\n", retval);
    exit (1);
  }

  printf ("%llu\n", ((unsigned long long) ext2fs_blocks_count(fs->super)) * EXT2_BLOCK_SIZE(fs->super));
}

[tbzatek]

I think we really should fix dumpe2fs or stop using it. Here is a potential fix: tytso/e2fsprogs#122

Nice!

One other major reason for making the property value retrieval on demand was to relieve I/O traffic. In practice, all other properties were retrieved from the (cached) udev database. In small systems this was not a big issue, the problem was daemon startup and first enumeration in case of large number of block devices.

We've had bugreports about the daemon not starting up in a reasonable time (30+ sec.) when autostarted from a first D-Bus call, resulting in the gvfs udisks2 volume monitor bailing out, falling back to local GIO unix monitoring. This happened on a system with rotational disks during higher load upon system startup.

[vojtechtrefny]

Related: libblkid now has two new filesystem properties/tags: FSSIZE and FSLASTBLOCK (not yet released) which we potentially could use for getting filesystem size, it will be also likely available in udev (which just calls blkid) so we could get these "for free" without calling libblockdev.

[mvollmer]

libblkid now has two now filesystem two properties/tags: FSSIZE and util-linux/util-linux#1665

Nice!

[tbzatek]

I've tried to hack a fix for the property change notification - see #1042.
@mvollmer: do you have any chance to test this please? I have just been watching dbus-monitor output but the client D-Bus bindings may behave in various ways. Let's just hope that with this change we'd be conforming with the D-Bus specifications with relation to clients out there.

[tbzatek]

ping @mvollmer - any chance to test #1042 please?