Use bytearray instead of array.array

I'm just gonna leave this here:

    >>> timeit.timeit("array.array(u'B', itertools.repeat(0, 4096))",
                      number=10000,
                      setup="import array; import itertools")
    3.422340818680823

    >>> timeit.timeit("a=bytearray(4096)", number=10000)
    0.0034010084345936775

Yes, you're seeing it right. 1000x faster. Especially for the block
group searches, which we are doing a lot of separately each time, this
makes a huge difference.

For a real life benchmark... On a large filesystem with >40k blockgroups
I have this reduces the time to retrieve and list all the items about
them (all info in disk cache) from 18 to 3 seconds.

btrfs/crc32c.py

@@ -16,8 +16,6 @@
 # Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
 # Boston, MA 02110-1301 USA
 
-import array
-
 table = (
     0x00000000, 0xf26b8303, 0xe13b70f7, 0x1350f3f4,
     0xc79a971f, 0x35f1141c, 0x26a1e7e8, 0xd4ca64eb,
@@ -87,7 +85,7 @@
 
 
 def name_hash(data):
-    if not isinstance(data, (array.array, bytearray)):
+    if not isinstance(data, (bytes, bytearray)):
         data = bytes(data, 'utf-8')
     crc = 4294967294  # (u32)~1
     for char in data:

btrfs/ioctl.py

@@ -19,7 +19,6 @@
 from collections import namedtuple
 import array
 import fcntl
-import itertools
 import platform
 import struct
 import uuid
@@ -93,10 +92,6 @@ def _IOWR(_type, nr, _struct):
 import btrfs.ctree  # noqa
 
 
-def create_buf(size=4096):
-    return array.array(u'B', itertools.repeat(0, size))
-
-
 ioctl_fs_info_args = struct.Struct('=QQ16sLLL980x')
 IOC_FS_INFO = _IOR(BTRFS_IOCTL_MAGIC, 31, ioctl_fs_info_args)
 
@@ -114,7 +109,7 @@ def __str__(self):
 
 
 def fs_info(fd):
-    buf = create_buf(ioctl_fs_info_args.size)
+    buf = bytearray(ioctl_fs_info_args.size)
     fcntl.ioctl(fd, IOC_FS_INFO, buf)
     return FsInfo(buf)
 
@@ -136,7 +131,7 @@ def __str__(self):
 
 
 def dev_info(fd, devid):
-    buf = create_buf(ioctl_dev_info_args.size)
+    buf = bytearray(ioctl_dev_info_args.size)
     ioctl_dev_info_args.pack_into(buf, 0, devid, b'', 0, 0, b'')
     fcntl.ioctl(fd, IOC_DEV_INFO, buf)
     return DevInfo(buf)
@@ -160,7 +155,7 @@ def __str__(self):
 
 
 def dev_stats(fd, devid, reset=False):
-    buf = create_buf(ioctl_get_dev_stats.size)
+    buf = bytearray(ioctl_get_dev_stats.size)
     ioctl_get_dev_stats.pack_into(buf, 0, devid, 5, int(reset), 0, 0, 0, 0, 0)
     fcntl.ioctl(fd, IOC_GET_DEV_STATS, buf)
     return DevStats(buf)
@@ -190,15 +185,15 @@ def __str__(self):
 
 
 def space_args(fd):
-    buf = create_buf(ioctl_space_args.size)
+    buf = bytearray(ioctl_space_args.size)
     fcntl.ioctl(fd, IOC_SPACE_INFO, buf)
     return SpaceArgs(*ioctl_space_args.unpack(buf))
 
 
 def space_info(fd):
     args = space_args(fd)
     buf_size = ioctl_space_args.size + ioctl_space_info.size * args.total_spaces
-    buf = create_buf(buf_size)
+    buf = bytearray(buf_size)
     ioctl_space_args.pack_into(buf, 0, args.total_spaces, 0)
     fcntl.ioctl(fd, IOC_SPACE_INFO, buf)
     return [SpaceInfo(buf, pos)
@@ -241,9 +236,9 @@ def search_v2(fd, tree, min_key=None, max_key=None,
     if _v2:
         if buf_size is None:
             buf_size = 16384
-        buf = create_buf(ioctl_search_args_v2.size + buf_size)
+        buf = bytearray(ioctl_search_args_v2.size + buf_size)
     else:
-        buf = create_buf(4096)
+        buf = bytearray(4096)
     while min_key <= max_key and result_nr_items != 0 and wanted_nr_items > 0:
         pos = 0
         ioctl_search_key.pack_into(buf, pos, tree,
@@ -283,9 +278,9 @@ def search_v2(fd, tree, min_key=None, max_key=None,
 
 def logical_to_ino(fd, vaddr, bufsize=4096):
     bufsize = min(bufsize, 65536)
-    inodes_buf = create_buf(bufsize)
+    inodes_buf = array.array(u'B', bytearray(bufsize))
     inodes_ptr = inodes_buf.buffer_info()[0]
-    args = create_buf(ioctl_logical_ino_args.size)
+    args = bytearray(ioctl_logical_ino_args.size)
     ioctl_logical_ino_args.pack_into(args, 0, vaddr, bufsize, inodes_ptr)
     fcntl.ioctl(fd, IOC_LOGICAL_INO, args)
     bytes_left, bytes_missing, elem_cnt, elem_missed = data_container.unpack_from(inodes_buf, 0)
@@ -303,7 +298,7 @@ def logical_to_ino(fd, vaddr, bufsize=4096):
 
 
 def ino_lookup(fd, treeid=0, objectid=FIRST_FREE_OBJECTID):
-    args = create_buf(ioctl_ino_lookup_args.size)
+    args = bytearray(ioctl_ino_lookup_args.size)
     ioctl_ino_lookup_args.pack_into(args, 0, treeid, objectid, b'')
     fcntl.ioctl(fd, IOC_INO_LOOKUP, args)
     treeid, _, name_bytes = ioctl_ino_lookup_args.unpack_from(args, 0)