ext4: Update inode i_size after the preallocation

Currently in ext4_fallocate we would update inode size, c_time and sync
the file with every partial allocation which is entirely unnecessary. It
is true that if the crash happens in the middle of truncate we might end
up with unchanged i size, or c_time which I do not think is really a
problem - it does not mean file system corruption in any way. Note that
xfs is doing things the same way e.g. update all of the mentioned after
the allocation is done.

This commit moves all the updates after the allocation is done. In
addition we also need to change m_time as not only inode has been change
bot also data regions might have changed (unwritten extents). However
m_time will be only updated when i_size changed.

Also we do not need to be paranoid about changing the c_time only if the
actual allocation have happened, we can change it even if we try to
allocate only to find out that there are already block allocated. It's
not really a big deal and it will save us some additional complexity.

Also use ext4_debug, instead of ext4_warning in #ifdef EXT4FS_DEBUG
section.

Signed-off-by: Lukas Czerner <lczerner@redhat.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu&gt;->
--
v3: Do not remove the code to set EXT4_INODE_EOFBLOCKS flag

 fs/ext4/extents.c | 96 ++++++++++++++++++++++++-------------------------------
 1 file changed, 42 insertions(+), 54 deletions(-)