Android系统Recovery工作原理3-- 升级包的制作

㈡下面我们分析ota_from_target_files这个python脚本是怎样生成最终zip包的。先讲这个脚本的代码贴出来如下：

import sys
if sys.hexversion < 0x02040000:
print >> sys.stderr, "Python 2.4 or newer is required."
sys.exit(1)
import copy
import errno
import os
import re
import sha
import subprocess
import tempfile
import time
import zipfile
import common
import edify_generator
OPTIONS = common.OPTIONS
OPTIONS.package_key = "build/target/product/security/testkey"
OPTIONS.incremental_source = None
OPTIONS.require_verbatim = set()
OPTIONS.prohibit_verbatim = set(("system/build.prop",))
OPTIONS.patch_threshold = 0.95
OPTIONS.wipe_user_data = False
OPTIONS.omit_prereq = False
OPTIONS.extra_script = None
OPTIONS.worker_threads = 3
def MostPopularKey(d, default):
"""Given a dict, return the key corresponding to the largest
value. Returns 'default' if the dict is empty."""
x = [(v, k) for (k, v) in d.iteritems()]
if not x: return default
x.sort()
return x[-1][1]
def IsSymlink(info):
"""Return true if the zipfile.ZipInfo object passed in represents a
symlink."""
return (info.external_attr >> 16) == 0120777
class Item:
"""Items represent the metadata (user, group, mode) of files and
directories in the system image."""
ITEMS = {}
def __init__(self, name, dir=False):
self.name = name
self.uid = None
self.gid = None
self.mode = None
self.dir = dir
if name:
self.parent = Item.Get(os.path.dirname(name), dir=True)
self.parent.children.append(self)
else:
self.parent = None
if dir:
self.children = []
def Dump(self, indent=0):
if self.uid is not None:
print "%s%s %d %d %o" % (" "*indent, self.name, self.uid, self.gid, self.mode)
else:
print "%s%s %s %s %s" % (" "*indent, self.name, self.uid, self.gid, self.mode)
if self.dir:
print "%s%s" % (" "*indent, self.descendants)
print "%s%s" % (" "*indent, self.best_subtree)
for i in self.children:
i.Dump(indent=indent+1)
@classmethod
def Get(cls, name, dir=False):
if name not in cls.ITEMS:
cls.ITEMS[name] = Item(name, dir=dir)
return cls.ITEMS[name]
@classmethod
def GetMetadata(cls, input_zip):
try:
# See if the target_files contains a record of what the uid,
# gid, and mode is supposed to be.
output = input_zip.read("META/filesystem_config.txt")
except KeyError:
# Run the external 'fs_config' program to determine the desired
# uid, gid, and mode for every Item object. Note this uses the
# one in the client now, which might not be the same as the one
# used when this target_files was built.
p = common.Run(["fs_config"], stdin=subprocess.PIPE,
stdout=subprocess.PIPE, stderr=subprocess.PIPE)
suffix = { False: "", True: "/" }
input = "".join(["%s%s\n" % (i.name, suffix[i.dir])
for i in cls.ITEMS.itervalues() if i.name])
output, error = p.communicate(input)
assert not error
for line in output.split("\n"):
if not line: continue
name, uid, gid, mode = line.split()
i = cls.ITEMS.get(name, None)
if i is not None:
i.uid = int(uid)
i.gid = int(gid)
i.mode = int(mode, 8)
if i.dir:
i.children.sort(key=lambda i: i.name)
# set metadata for the files generated by this script.
i = cls.ITEMS.get("system/recovery-from-boot.p", None)
if i: i.uid, i.gid, i.mode = 0, 0, 0644
i = cls.ITEMS.get("system/etc/install-recovery.sh", None)
if i: i.uid, i.gid, i.mode = 0, 0, 0544
def CountChildMetadata(self):
"""Count up the (uid, gid, mode) tuples for all children and
determine the best strategy for using set_perm_recursive and
set_perm to correctly chown/chmod all the files to their desired
values. Recursively calls itself for all descendants.
Returns a dict of {(uid, gid, dmode, fmode): count} counting up
all descendants of this node. (dmode or fmode may be None.) Also
sets the best_subtree of each directory Item to the (uid, gid,
dmode, fmode) tuple that will match the most descendants of that
Item.
"""
assert self.dir
d = self.descendants = {(self.uid, self.gid, self.mode, None): 1}
for i in self.children:
if i.dir:
for k, v in i.CountChildMetadata().iteritems():
d[k] = d.get(k, 0) + v
else:
k = (i.uid, i.gid, None, i.mode)
d[k] = d.get(k, 0) + 1
# Find the (uid, gid, dmode, fmode) tuple that matches the most
# descendants.
# First, find the (uid, gid) pair that matches the most
# descendants.
ug = {}
for (uid, gid, _, _), count in d.iteritems():
ug[(uid, gid)] = ug.get((uid, gid), 0) + count
ug = MostPopularKey(ug, (0, 0))
# Now find the dmode and fmode that match the most descendants
# with that (uid, gid), and choose those.
best_dmode = (0, 0755)
best_fmode = (0, 0644)
for k, count in d.iteritems():
if k[:2] != ug: continue
if k[2] is not None and count >= best_dmode[0]: best_dmode = (count, k[2])
if k[3] is not None and count >= best_fmode[0]: best_fmode = (count, k[3])
self.best_subtree = ug + (best_dmode[1], best_fmode[1])
return d
def SetPermissions(self, script):
"""Append set_perm/set_perm_recursive commands to 'script' to
set all permissions, users, and groups for the tree of files
rooted at 'self'."""
self.CountChildMetadata()
def recurse(item, current):
# current is the (uid, gid, dmode, fmode) tuple that the current
# item (and all its children) have already been set to. We only
# need to issue set_perm/set_perm_recursive commands if we're
# supposed to be something different.
if item.dir:
if current != item.best_subtree:
script.SetPermissionsRecursive("/"+item.name, *item.best_subtree)
current = item.best_subtree
if item.uid != current[0] or item.gid != current[1] or \
item.mode != current[2]:
script.SetPermissions("/"+item.name, item.uid, item.gid, item.mode)
for i in item.children:
recurse(i, current)
else:
if item.uid != current[0] or item.gid != current[1] or \
item.mode != current[3]:
script.SetPermissions("/"+item.name, item.uid, item.gid, item.mode)
recurse(self, (-1, -1, -1, -1))
def CopySystemFiles(input_zip, output_zip=None,
substitute=None):
"""Copies files underneath system/ in the input zip to the output
zip. Populates the Item class with their metadata, and returns a
list of symlinks. output_zip may be None, in which case the copy is
skipped (but the other side effects still happen). substitute is an
optional dict of {output filename: contents} to be output instead of
certain input files.
"""
symlinks = []
for info in input_zip.infolist():
if info.filename.startswith("SYSTEM/"):
basefilename = info.filename[7:]
if IsSymlink(info):
symlinks.append((input_zip.read(info.filename),
"/system/" + basefilename))
else:
info2 = copy.copy(info)
fn = info2.filename = "system/" + basefilename
if substitute and fn in substitute and substitute[fn] is None:
continue
if output_zip is not None:
if substitute and fn in substitute:
data = substitute[fn]
else:
data = input_zip.read(info.filename)
output_zip.writestr(info2, data)
if fn.endswith("/"):
Item.Get(fn[:-1], dir=True)
else:
Item.Get(fn, dir=False)
symlinks.sort()
return symlinks
def SignOutput(temp_zip_name, output_zip_name):
key_passwords = common.GetKeyPasswords([OPTIONS.package_key])
pw = key_passwords[OPTIONS.package_key]
common.SignFile(temp_zip_name, output_zip_name, OPTIONS.package_key, pw,
whole_file=True)
def AppendAssertions(script, input_zip):
device = GetBuildProp("ro.product.device", input_zip)
script.AssertDevice(device)
def MakeRecoveryPatch(output_zip, recovery_img, boot_img):
"""Generate a binary patch that creates the recovery image starting
with the boot image. (Most of the space in these images is just the
kernel, which is identical for the two, so the resulting patch
should be efficient.) Add it to the output zip, along with a shell
script that is run from init.rc on first boot to actually do the
patching and install the new recovery image.
recovery_img and boot_img should be File objects for the
corresponding images.
Returns an Item for the shell script, which must be made
executable.
"""
d = common.Difference(recovery_img, boot_img)
_, _, patch = d.ComputePatch()
common.ZipWriteStr(output_zip, "recovery/recovery-from-boot.p", patch)
Item.Get("system/recovery-from-boot.p", dir=False)
boot_type, boot_device = common.GetTypeAndDevice("/boot", OPTIONS.info_dict)
recovery_type, recovery_device = common.GetTypeAndDevice("/recovery", OPTIONS.info_dict)
# Images with different content will have a different first page, so
# we check to see if this recovery has already been installed by
# testing just the first 2k.
HEADER_SIZE = 2048
header_sha1 = sha.sha(recovery_img.data[:HEADER_SIZE]).hexdigest()
sh = """#!/system/bin/sh
if ! applypatch -c %(recovery_type)s:%(recovery_device)s:%(header_size)d:%(header_sha1)s; then
log -t recovery "Installing new recovery image"
applypatch %(boot_type)s:%(boot_device)s:%(boot_size)d:%(boot_sha1)s %(recovery_type)s:%(recovery_device)s %(recovery_sha1)s %(recovery_size)d %(boot_sha1)s:/system/recovery-from-boot.p
else
log -t recovery "Recovery image already installed"
fi
""" % { 'boot_size': boot_img.size,
'boot_sha1': boot_img.sha1,
'header_size': HEADER_SIZE,
'header_sha1': header_sha1,
'recovery_size': recovery_img.size,
'recovery_sha1': recovery_img.sha1,
'boot_type': boot_type,
'boot_device': boot_device,
'recovery_type': recovery_type,
'recovery_device': recovery_device,
}
common.ZipWriteStr(output_zip, "recovery/etc/install-recovery.sh", sh)
return Item.Get("system/etc/install-recovery.sh", dir=False)
def WriteFullOTAPackage(input_zip, output_zip):
# TODO: how to determine this? We don't know what version it will
# be installed on top of. For now, we expect the API just won't
# change very often.
script = edify_generator.EdifyGenerator(3, OPTIONS.info_dict)
metadata = {"post-build": GetBuildProp("ro.build.fingerprint", input_zip),
"pre-device": GetBuildProp("ro.product.device", input_zip),
"post-timestamp": GetBuildProp("ro.build.date.utc", input_zip),
}
device_specific = common.DeviceSpecificParams(
input_zip=input_zip,
input_version=OPTIONS.info_dict["recovery_api_version"],
output_zip=output_zip,
script=script,
input_tmp=OPTIONS.input_tmp,
metadata=metadata,
info_dict=OPTIONS.info_dict)
if not OPTIONS.omit_prereq:
ts = GetBuildProp("ro.build.date.utc", input_zip)
script.AssertOlderBuild(ts)
AppendAssertions(script, input_zip)
device_specific.FullOTA_Assertions()
script.ShowProgress(0.5, 0)
if OPTIONS.wipe_user_data:
script.FormatPartition("/data")
script.FormatPartition("/system")
script.Mount("/system")
script.UnpackPackageDir("recovery", "/system")
script.UnpackPackageDir("system", "/system")
symlinks = CopySystemFiles(input_zip, output_zip)
script.MakeSymlinks(symlinks)
boot_img = common.File("boot.img", common.BuildBootableImage(
os.path.join(OPTIONS.input_tmp, "BOOT")))
recovery_img = common.File("recovery.img", common.BuildBootableImage(
os.path.join(OPTIONS.input_tmp, "RECOVERY")))
MakeRecoveryPatch(output_zip, recovery_img, boot_img)
Item.GetMetadata(input_zip)
Item.Get("system").SetPermissions(script)
common.CheckSize(boot_img.data, "boot.img", OPTIONS.info_dict)
common.ZipWriteStr(output_zip, "boot.img", boot_img.data)
script.ShowProgress(0.2, 0)
script.ShowProgress(0.2, 10)
script.WriteRawImage("/boot", "boot.img")
script.ShowProgress(0.1, 0)
device_specific.FullOTA_InstallEnd()
if OPTIONS.extra_script is not None:
script.AppendExtra(OPTIONS.extra_script)
script.UnmountAll()
script.AddToZip(input_zip, output_zip)
WriteMetadata(metadata, output_zip)
def WriteMetadata(metadata, output_zip):
common.ZipWriteStr(output_zip, "META-INF/com/android/metadata",
"".join(["%s=%s\n" % kv
for kv in sorted(metadata.iteritems())]))
def LoadSystemFiles(z):
"""Load all the files from SYSTEM/... in a given target-files
ZipFile, and return a dict of {filename: File object}."""
out = {}
for info in z.infolist():
if info.filename.startswith("SYSTEM/") and not IsSymlink(info):
fn = "system/" + info.filename[7:]
data = z.read(info.filename)
out[fn] = common.File(fn, data)
return out
def GetBuildProp(property, z):
"""Return the fingerprint of the build of a given target-files
ZipFile object."""
bp = z.read("SYSTEM/build.prop")
if not property:
return bp
m = re.search(re.escape(property) + r"=(.*)\n", bp)
if not m:
raise common.ExternalError("couldn't find %s in build.prop" % (property,))
return m.group(1).strip()
def WriteIncrementalOTAPackage(target_zip, source_zip, output_zip):
source_version = OPTIONS.source_info_dict["recovery_api_version"]
target_version = OPTIONS.target_info_dict["recovery_api_version"]
if source_version == 0:
print ("WARNING: generating edify script for a source that "
"can't install it.")
script = edify_generator.EdifyGenerator(source_version, OPTIONS.info_dict)
metadata = {"pre-device": GetBuildProp("ro.product.device", source_zip),
"post-timestamp": GetBuildProp("ro.build.date.utc", target_zip),
}
device_specific = common.DeviceSpecificParams(
source_zip=source_zip,
source_version=source_version,
target_zip=target_zip,
target_version=target_version,
output_zip=output_zip,
script=script,
metadata=metadata,
info_dict=OPTIONS.info_dict)
print "Loading target..."
target_data = LoadSystemFiles(target_zip)
print "Loading source..."
source_data = LoadSystemFiles(source_zip)
verbatim_targets = []
patch_list = []
diffs = []
largest_source_size = 0
for fn in sorted(target_data.keys()):
tf = target_data[fn]
assert fn == tf.name
sf = source_data.get(fn, None)
if sf is None or fn in OPTIONS.require_verbatim:
# This file should be included verbatim
if fn in OPTIONS.prohibit_verbatim:
raise common.ExternalError(""%s" must be sent verbatim" % (fn,))
print "send", fn, "verbatim"
tf.AddToZip(output_zip)
verbatim_targets.append((fn, tf.size))
elif tf.sha1 != sf.sha1:
# File is different; consider sending as a patch
diffs.append(common.Difference(tf, sf))
else:
# Target file identical to source.
pass
common.ComputeDifferences(diffs)
for diff in diffs:
tf, sf, d = diff.GetPatch()
if d is None or len(d) > tf.size * OPTIONS.patch_threshold:
# patch is almost as big as the file; don't bother patching
tf.AddToZip(output_zip)
verbatim_targets.append((tf.name, tf.size))
else:
common.ZipWriteStr(output_zip, "patch/" + tf.name + ".p", d)
patch_list.append((tf.name, tf, sf, tf.size, sha.sha(d).hexdigest()))
largest_source_size = max(largest_source_size, sf.size)
source_fp = GetBuildProp("ro.build.fingerprint", source_zip)
target_fp = GetBuildProp("ro.build.fingerprint", target_zip)
metadata["pre-build"] = source_fp
metadata["post-build"] = target_fp
script.Mount("/system")
script.AssertSomeFingerprint(source_fp, target_fp)
source_boot = common.File("/tmp/boot.img",
common.BuildBootableImage(
os.path.join(OPTIONS.source_tmp, "BOOT")))
target_boot = common.File("/tmp/boot.img",
common.BuildBootableImage(
os.path.join(OPTIONS.target_tmp, "BOOT")))
updating_boot = (source_boot.data != target_boot.data)
source_recovery = common.File("system/recovery.img",
common.BuildBootableImage(
os.path.join(OPTIONS.source_tmp, "RECOVERY")))
target_recovery = common.File("system/recovery.img",
common.BuildBootableImage(
os.path.join(OPTIONS.target_tmp, "RECOVERY")))
updating_recovery = (source_recovery.data != target_recovery.data)
# Here's how we divide up the progress bar:
# 0.1 for verifying the start state (PatchCheck calls)
# 0.8 for applying patches (ApplyPatch calls)
# 0.1 for unpacking verbatim files, symlinking, and doing the
# device-specific commands.
AppendAssertions(script, target_zip)
device_specific.IncrementalOTA_Assertions()
script.Print("Verifying current system...")
script.ShowProgress(0.1, 0)
total_verify_size = float(sum([i[2].size for i in patch_list]) + 1)
if updating_boot:
total_verify_size += source_boot.size
so_far = 0
for fn, tf, sf, size, patch_sha in patch_list:
script.PatchCheck("/"+fn, tf.sha1, sf.sha1)
so_far += sf.size
script.SetProgress(so_far / total_verify_size)
if updating_boot:
d = common.Difference(target_boot, source_boot)
_, _, d = d.ComputePatch()
print "boot target: %d source: %d diff: %d" % (
target_boot.size, source_boot.size, len(d))
common.ZipWriteStr(output_zip, "patch/boot.img.p", d)
boot_type, boot_device = common.GetTypeAndDevice("/boot", OPTIONS.info_dict)
script.PatchCheck("%s:%s:%d:%s:%d:%s" %
(boot_type, boot_device,
source_boot.size, source_boot.sha1,
target_boot.size, target_boot.sha1))
so_far += source_boot.size
script.SetProgress(so_far / total_verify_size)
if patch_list or updating_recovery or updating_boot:
script.CacheFreeSpaceCheck(largest_source_size)
device_specific.IncrementalOTA_VerifyEnd()
script.Comment("---- start making changes here ----")
if OPTIONS.wipe_user_data:
script.Print("Erasing user data...")
script.FormatPartition("/data")
script.Print("Removing unneeded files...")
script.DeleteFiles(["/"+i[0] for i in verbatim_targets] +
["/"+i for i in sorted(source_data)
if i not in target_data] +
["/system/recovery.img"])
script.ShowProgress(0.8, 0)
total_patch_size = float(sum([i[1].size for i in patch_list]) + 1)
if updating_boot:
total_patch_size += target_boot.size
so_far = 0
script.Print("Patching system files...")
for fn, tf, sf, size, _ in patch_list:
script.ApplyPatch("/"+fn, "-", tf.size, tf.sha1, sf.sha1, "patch/"+fn+".p")
so_far += tf.size
script.SetProgress(so_far / total_patch_size)
if updating_boot:
# Produce the boot image by applying a patch to the current
# contents of the boot partition, and write it back to the
# partition.
script.Print("Patching boot image...")
script.ApplyPatch("%s:%s:%d:%s:%d:%s"
% (boot_type, boot_device,
source_boot.size, source_boot.sha1,
target_boot.size, target_boot.sha1),
"-",
target_boot.size, target_boot.sha1,
source_boot.sha1, "patch/boot.img.p")
so_far += target_boot.size
script.SetProgress(so_far / total_patch_size)
print "boot image changed; including."
else:
print "boot image unchanged; skipping."
if updating_recovery:
# Is it better to generate recovery as a patch from the current
# boot image, or from the previous recovery image? For large
# updates with significant kernel changes, probably the former.
# For small updates where the kernel hasn't changed, almost
# certainly the latter. We pick the first option. Future
# complicated schemes may let us effectively use both.
#
# A wacky possibility: as long as there is room in the boot
# partition, include the binaries and image files from recovery in
# the boot image (though not in the ramdisk) so they can be used
# as fodder for constructing the recovery image.
MakeRecoveryPatch(output_zip, target_recovery, target_boot)
script.DeleteFiles(["/system/recovery-from-boot.p",
"/system/etc/install-recovery.sh"])
print "recovery image changed; including as patch from boot."
else:
print "recovery image unchanged; skipping."
script.ShowProgress(0.1, 10)
target_symlinks = CopySystemFiles(target_zip, None)
target_symlinks_d = dict([(i[1], i[0]) for i in target_symlinks])
temp_script = script.MakeTemporary()
Item.GetMetadata(target_zip)
Item.Get("system").SetPermissions(temp_script)
# Note that this call will mess up the tree of Items, so make sure
# we're done with it.
source_symlinks = CopySystemFiles(source_zip, None)
source_symlinks_d = dict([(i[1], i[0]) for i in source_symlinks])
# Delete all the symlinks in source that aren't in target. This
# needs to happen before verbatim files are unpacked, in case a
# symlink in the source is replaced by a real file in the target.
to_delete = []
for dest, link in source_symlinks:
if link not in target_symlinks_d:
to_delete.append(link)
script.DeleteFiles(to_delete)
if verbatim_targets:
script.Print("Unpacking new files...")
script.UnpackPackageDir("system", "/system")
if updating_recovery:
script.Print("Unpacking new recovery...")
script.UnpackPackageDir("recovery", "/system")
script.Print("Symlinks and permissions...")
# Create all the symlinks that don't already exist, or point to
# somewhere different than what we want. Delete each symlink before
# creating it, since the 'symlink' command won't overwrite.
to_create = []
for dest, link in target_symlinks:
if link in source_symlinks_d:
if dest != source_symlinks_d[link]:
to_create.append((dest, link))
else:
to_create.append((dest, link))
script.DeleteFiles([i[1] for i in to_create])
script.MakeSymlinks(to_create)
# Now that the symlinks are created, we can set all the
# permissions.
script.AppendScript(temp_script)
# Do device-specific installation (eg, write radio image).
device_specific.IncrementalOTA_InstallEnd()
if OPTIONS.extra_script is not None:
scirpt.AppendExtra(OPTIONS.extra_script)
script.AddToZip(target_zip, output_zip)
WriteMetadata(metadata, output_zip)
def main(argv):
def option_handler(o, a):
if o in ("-b", "--board_config"):
pass # deprecated
elif o in ("-k", "--package_key"):
OPTIONS.package_key = a
elif o in ("-i", "--incremental_from"):
OPTIONS.incremental_source = a
elif o in ("-w", "--wipe_user_data"):
OPTIONS.wipe_user_data = True
elif o in ("-n", "--no_prereq"):
OPTIONS.omit_prereq = True
elif o in ("-e", "--extra_script"):
OPTIONS.extra_script = a
elif o in ("--worker_threads"):
OPTIONS.worker_threads = int(a)
else:
return False
return True
args = common.ParseOptions(argv, __doc__,
extra_opts="b:k:i:d:wne:",
extra_long_opts=["board_config=",
"package_key=",
"incremental_from=",
"wipe_user_data",
"no_prereq",
"extra_script=",
"worker_threads="],
extra_option_handler=option_handler)
if len(args) != 2:
common.Usage(__doc__)
sys.exit(1)
if OPTIONS.extra_script is not None:
OPTIONS.extra_script = open(OPTIONS.extra_script).read()
print "unzipping target target-files..."
OPTIONS.input_tmp = common.UnzipTemp(args[0])
OPTIONS.target_tmp = OPTIONS.input_tmp
input_zip = zipfile.ZipFile(args[0], "r")
OPTIONS.info_dict = common.LoadInfoDict(input_zip)
if OPTIONS.verbose:
print "--- target info ---"
common.DumpInfoDict(OPTIONS.info_dict)
if OPTIONS.device_specific is None:
OPTIONS.device_specific = OPTIONS.info_dict.get("tool_extensions", None)
if OPTIONS.device_specific is not None:
OPTIONS.device_specific = os.path.normpath(OPTIONS.device_specific)
print "using device-specific extensions in", OPTIONS.device_specific
if OPTIONS.package_key:
temp_zip_file = tempfile.NamedTemporaryFile()
output_zip = zipfile.ZipFile(temp_zip_file, "w",
compression=zipfile.ZIP_DEFLATED)
else:
output_zip = zipfile.ZipFile(args[1], "w",
compression=zipfile.ZIP_DEFLATED)
if OPTIONS.incremental_source is None:
WriteFullOTAPackage(input_zip, output_zip)
else:
print "unzipping source target-files..."
OPTIONS.source_tmp = common.UnzipTemp(OPTIONS.incremental_source)
source_zip = zipfile.ZipFile(OPTIONS.incremental_source, "r")
OPTIONS.target_info_dict = OPTIONS.info_dict
OPTIONS.source_info_dict = common.LoadInfoDict(source_zip)
if OPTIONS.verbose:
print "--- source info ---"
common.DumpInfoDict(OPTIONS.source_info_dict)
WriteIncrementalOTAPackage(input_zip, source_zip, output_zip)
output_zip.close()
if OPTIONS.package_key:
SignOutput(temp_zip_file.name, args[1])
temp_zip_file.close()
common.Cleanup()
print "done."
if __name__ == '__main__':
try:
common.CloseInheritedPipes()
main(sys.argv[1:])
except common.ExternalError, e:
print
print " ERROR: %s" % (e,)
print
sys.exit(1)

主函数main是python的入口函数，我们从main函数开始看，大概看一下main函数（脚本最后）里的流程就能知道脚本的执行过程了。

                                 ① 在main函数的开头，首先将用户设定的option选项存入OPTIONS变量中，它是一个python中的类。紧接着判断有没有额外的脚本，如果有就读入到OPTIONS变量中。
                                 ② 解压缩输入的zip包，即我们在上文生成的原始zip包。然后判断是否用到device-specific extensions（设备扩展）如果用到，随即读入到OPTIONS变量中。
                                 ③ 判断是否签名，然后判断是否有新内容的增量源，有的话就解压该增量源包放入一个临时变量中（source_zip）。自此，所有的准备工作已完毕，随即会调用该脚本中最主要的函数WriteFullOTAPackag e(input_zip,output_zip)
                                 ④ WriteFullOTAPackage函数的处理过程是先获得脚本的生成器。默认格式是edify。然后获得metadata元数据，此数据来至于Android的一些环境变量。然后获得设备配置参数比如api函数的版本。然后判断是否忽略时间戳。
                                 ⑤ WriteFullOTAPackage函数做完准备工作后就开始生成升级用的脚本文件(updater-script)了。生成脚本文件后将上一步获得的metadata元数据写入到输出包out_zip。
                                 ⑥至此一个完整的update.zip升级包就生成了。生成位置在：out/target/product/tcc8800 /full_tcc8800_evm-ota-eng.mumu.20120315.155326.zip。将升级包拷贝到SD卡中就可以用来升级了。

四、 Android OTA增量包update.zip的生成

在上面的过程中生成的update.zip升级包是全部系统的升级包。大小有95M多，在实际升级中，我们只希望能够升级我们改变的那部分内容。这就需要使用增量包来升级。生成增量包的过程也需要上文中提到的ota_from_target_files的参与。

下面是制作update.zip增量包的过程。

            ① 在源码根目录下依次执行下列命令
               $ . build/envsetup.sh
               $ lunch 选择17
               $ make
               $ make otapackage
               执行上面的命令后会在out/target/product/tcc8800/下生成我们第一个系统升级包。我们先将其命名为A.zip
            ② 在源码中修改我们需要改变的部分，比如修改内核配置，增加新的驱动等等。修改后再一次执行上面的命令。就会生成第二个我们修改后生成的update.zip升级包。将其命名为B.zip。

③ 在上文中我们看了ota_from_target_files.py脚本的使用帮助，其中选项-i就是用来生成差分增量包的。使用方法是以上面的 A.zip 和B.zip包作为输入，以update.zip包作为输出。生成的update.zip就是我们最后需要的增量包。

具体使用方式是：将上述两个包拷贝到源码根目录下，然后执行下面的命令。

$ ./build/tools/releasetools/ota_from_target_files -i A.zip B.zip update.zip。

在执行上述命令时会出现未找到recovery_api_version的错误。原因是在执行上面的脚本时如果使用选项i则会调用 WriteIncrementalOTAPackage会从A包和B包中的META目录下搜索misc_info.txt来读取 recovery_api_version的值。但是在执行make otapackage命令时生成的update.zip包中没有这个目录更没有这个文档。

此时我们就需要使用执行make otapackage生成的原始的zip包。这个包的位置在out/target/product/tcc8800/obj/PACKAGING/target_files_intermediates/目录下，它是在用命令make otapackage之后的中间生产物，是最原始的升级包。我们将两次编译的生成的原始包分别重命名为A.zip和B.zip，并拷贝到SD卡根目录下重复执行上面的命令：

$ ./build/tools/releasetools/ota_form_target_files -i A.zip B.zip update.zip。

在上述命令即将执行完毕时，device/telechips/common/releasetools.py会调用IncrementalOTA_InstallEnd,在这个函数中读取包中的RADIO/bootloader.img。

而包中是没有这个目录和bootloader.img的。所以执行失败，未能生成对应的update.zip。可能与我们未修改bootloader（升级firmware）有关。

秒客网

Android系统Recovery工作原理3-- 升级包的制作

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