btrfs-progs: map-logical: Rework map-logical logics

btrfs-progs: map-logical: Rework map-logical logics

[BUG]
The original map-logical has the following problems:
1) Assert if we pass any tree root bytenr.
The problem is easy to trigger, here the number 29622272 is the bytenr of tree root:

 # btrfs-map-logical -l 29622272 /dev/sda6
 mirror 1 logical 29622272 physical 38010880 device /dev/sda6
 mirror 2 logical 29622272 physical 1111752704 device /dev/sda6
 extent_io.c:582: free_extent_buffer: Assertion `eb->refs < 0` failed.
 btrfs-map-logical[0x41c464]
 btrfs-map-logical(free_extent_buffer+0xc0)[0x41cf10]
 btrfs-map-logical(btrfs_release_all_roots+0x59)[0x40e649]
 btrfs-map-logical(close_ctree+0x1aa)[0x40f51a]
 btrfs-map-logical(main+0x387)[0x4077c7]
 /usr/lib/libc.so.6(__libc_start_main+0xf0)[0x7f80a5562790]
 btrfs-map-logical(_start+0x29)[0x4078f9]

The problem is that, btrfs-map-logical always use sectorsize as default
block size to call alloc_extent_buffer.
And when it failes to find the block with the same size, it will free
the extent buffer in a incorrect method(Free and create a new one with
refs == 1).

2) Will return map result for non-exist extent.

 # btrfs-map-logical -l 1 -b 123456 /dev/sda6
 mirror 1 logical 1 physical 1 device /dev/sda6
 mirror 1 logical 4097 physical 4097 device /dev/sda6
 mirror 1 logical 8193 physical 8193 device /dev/sda6
 ...

Normally, before bytenr 12582912, there should be no extent as that's
the mkfs time temp metadata/system chunk.

But map-logical will still map them out.

Not to mention the 1 offset among all results.

[FIX]
This patch will rework the whole map logical by the following methods:
1) Always do things inside a extent
Even under the following case, map logical will only return covered
range in existing extents.

	|<------ range given ------->|
|<-Extent A->|	|<-Extent B->|	|<---Extent C->|
Result:
	|<-->|	|<---------->|	|<-->|

So with this patch, we will search extent tree to ensure all operation
are inside a extent before we do some stupid things.

2) No direct call on alloc_extent_buffer function.

That low-level function shouldn't be called at such high level.
It's only designed for low-level tree operation.

So in this patch we will only use safe high level functions avoid such
problem.

[RESULT]
With this patch, no assert will be triggered and better handle on
non-exist extents.

 # btrfs-map-logical -l 29622272 /dev/sda6
 mirror 1 logical 29622272 physical 38010880 device /dev/sda6
 mirror 2 logical 29622272 physical 1111752704 device /dev/sda6

 # btrfs-map-logical -l 1 -b 123456 /dev/sda6
 No extent found at range [1,123457)

Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.cz>