Full local backup infrastructure
This is the basic infrastructure for pulling a full(*) backup of the
device's data over an adb(**) connection to the local device. The
basic process consists of these interacting pieces:
1. The framework's BackupManagerService, which coordinates the
collection of app data and routing to the destination.
2. A new framework-provided BackupAgent implementation called
FullBackupAgent, which is instantiated in the target applications'
processes in turn, and knows how to emit a datastream that contains
all of the app's saved data files.
3. A new shell-level program called "bu" that is used to bridge from
adb to the framework's Backup Manager.
4. adb itself, which now knows how to use 'bu' to kick off a backup
operation and pull the resulting data stream to the desktop host.
5. A system-provided application that verifies with the user that
an attempted backup/restore operation is in fact expected and to
be allowed.
The full agent implementation is not used during normal operation of
the delta-based app-customized remote backup process. Instead it's
used during user-confirmed *full* backup of applications and all their
data to a local destination, e.g. via the adb connection.
The output format is 'tar'. This makes it very easy for the end
user to examine the resulting dataset, e.g. for purpose of extracting
files for debug purposes; as well as making it easy to contemplate
adding things like a direct gzip stage to the data pipeline during
backup/restore. It also makes it convenient to construct and maintain
synthetic backup datasets for testing purposes.
Within the tar format, certain artificial conventions are used.
All files are stored within top-level directories according to
their semantic origin:
apps/pkgname/a/ : Application .apk file itself
apps/pkgname/obb/: The application's associated .obb containers
apps/pkgname/f/ : The subtree rooted at the getFilesDir() location
apps/pkgname/db/ : The subtree rooted at the getDatabasePath() parent
apps/pkgname/sp/ : The subtree rooted at the getSharedPrefsFile() parent
apps/pkgname/r/ : Files stored relative to the root of the app's file tree
apps/pkgname/c/ : Reserved for the app's getCacheDir() tree; not stored.
For each package, the first entry in the tar stream is a file called
"_manifest", nominally rooted at apps/pkgname. This file contains some
metadata about the package whose data is stored in the archive.
The contents of shared storage can optionally be included in the tar
stream. It is placed in the synthetic location:
shared/...
uid/gid are ignored; app uids are assigned at install time, and the
app's data is handled from within its own execution environment, so
will automatically have the app's correct uid.
Forward-locked .apk files are never backed up. System-partition
.apk files are not backed up unless they have been overridden by a
post-factory upgrade, in which case the current .apk *is* backed up --
i.e. the .apk that matches the on-disk data. The manifest preceding
each application's portion of the tar stream provides version numbers
and signature blocks for version checking, as well as an indication
of whether the restore logic should expect to install the .apk before
extracting the data.
System packages can designate their own full backup agents. This is
to manage things like the settings provider which (a) cannot be shut
down on the fly in order to do a clean snapshot of their file trees,
and (b) manage data that is not only irrelevant but actively hostile
to non-identical devices -- CDMA telephony settings would seriously
mess up a GSM device if emplaced there blind, for example.
When a full backup or restore is initiated from adb, the system will
present a confirmation UI that the user must explicitly respond to
within a short [~ 30 seconds] timeout. This is to avoid the
possibility of malicious desktop-side software secretly grabbing a copy
of all the user's data for nefarious purposes.
(*) The backup is not strictly a full mirror. In particular, the
settings database is not cloned; it is handled the same way that
it is in cloud backup/restore. This is because some settings
are actively destructive if cloned onto a different (or
especially a different-model) device: telephony settings and
AndroidID are good examples of this.
(**) On the framework side it doesn't care that it's adb; it just
sends the tar stream to a file descriptor. This can easily be
retargeted around whatever transport we might decide to use
in the future.
KNOWN ISSUES:
* the security UI is desperately ugly; no proper designs have yet
been done for it
* restore is not yet implemented
* shared storage backup is not yet implemented
* symlinks aren't yet handled, though some infrastructure for
dealing with them has been put in place.
Change-Id: Ia8347611e23b398af36ea22c36dff0a276b1ce91
diff --git a/libs/utils/BackupHelpers.cpp b/libs/utils/BackupHelpers.cpp
index 4ad9b51..ad4a308 100644
--- a/libs/utils/BackupHelpers.cpp
+++ b/libs/utils/BackupHelpers.cpp
@@ -442,6 +442,184 @@
return 0;
}
+// Utility function, equivalent to stpcpy(): perform a strcpy, but instead of
+// returning the initial dest, return a pointer to the trailing NUL.
+static char* strcpy_ptr(char* dest, const char* str) {
+ if (dest && str) {
+ while ((*dest = *str) != 0) {
+ dest++;
+ str++;
+ }
+ }
+ return dest;
+}
+
+int write_tarfile(const String8& packageName, const String8& domain,
+ const String8& rootpath, const String8& filepath, BackupDataWriter* writer)
+{
+ // In the output stream everything is stored relative to the root
+ const char* relstart = filepath.string() + rootpath.length();
+ if (*relstart == '/') relstart++; // won't be true when path == rootpath
+ String8 relpath(relstart);
+
+ // Too long a name for the ustar format?
+ // "apps/" + packagename + '/' + domainpath < 155 chars
+ // relpath < 100 chars
+ if ((5 + packageName.length() + 1 + domain.length() >= 155) || (relpath.length() >= 100)) {
+ LOGE("Filename [%s] too long, skipping", relpath.string());
+ return -1;
+ }
+
+ int err = 0;
+ struct stat64 s;
+ if (lstat64(filepath.string(), &s) != 0) {
+ err = errno;
+ LOGE("Error %d (%s) from lstat64(%s)", err, strerror(err), filepath.string());
+ return err;
+ }
+
+ const int isdir = S_ISDIR(s.st_mode);
+
+ // !!! TODO: use mmap when possible to avoid churning the buffer cache
+ // !!! TODO: this will break with symlinks; need to use readlink(2)
+ int fd = open(filepath.string(), O_RDONLY);
+ if (fd < 0) {
+ err = errno;
+ LOGE("Error %d (%s) from open(%s)", err, strerror(err), filepath.string());
+ return err;
+ }
+
+ // read/write up to this much at a time.
+ const size_t BUFSIZE = 32 * 1024;
+
+ char* buf = new char[BUFSIZE];
+ if (buf == NULL) {
+ LOGE("Out of mem allocating transfer buffer");
+ err = ENOMEM;
+ goto done;
+ }
+
+ // Good to go -- first construct the standard tar header at the start of the buffer
+ memset(buf, 0, 512); // tar header is 512 bytes
+
+ // Magic fields for the ustar file format
+ strcat(buf + 257, "ustar");
+ strcat(buf + 263, "00");
+
+ {
+ // Prefix and main relative path. Path lengths have been preflighted.
+
+ // [ 345 : 155 ] filename path prefix [ustar]
+ //
+ // packagename and domain can each be empty.
+ char* cp = buf + 345;
+ if (packageName.length() > 0) {
+ // it's an app; so prefix with "apps/packagename/"
+ cp = strcpy_ptr(cp, "apps/");
+ cp = strcpy_ptr(cp, packageName.string());
+ }
+
+ if (domain.length() > 0) {
+ // only need a / if there was a package name
+ if (packageName.length() > 0) *cp++ = '/';
+ cp = strcpy_ptr(cp, domain.string());
+ }
+
+ // [ 0 : 100 ]; file name/path
+ strncpy(buf, relpath.string(), 100);
+
+ LOGI(" Name: %s/%s", buf + 345, buf);
+ }
+
+ // [ 100 : 8 ] file mode
+ snprintf(buf + 100, 8, "0%o", s.st_mode);
+
+ // [ 108 : 8 ] uid -- ignored in Android format; uids are remapped at restore time
+ // [ 116 : 8 ] gid -- ignored in Android format
+ snprintf(buf + 108, 8, "0%lo", s.st_uid);
+ snprintf(buf + 116, 8, "0%lo", s.st_gid);
+
+ // [ 124 : 12 ] file size in bytes
+ snprintf(buf + 124, 12, "0%llo", s.st_size);
+
+ // [ 136 : 12 ] last mod time as a UTC time_t
+ snprintf(buf + 136, 12, "%0lo", s.st_mtime);
+
+ // [ 148 : 8 ] checksum -- to be calculated with this field as space chars
+ memset(buf + 148, ' ', 8);
+
+ // [ 156 : 1 ] link/file type
+ uint8_t type;
+ if (isdir) {
+ type = '5'; // tar magic: '5' == directory
+ } else if (S_ISREG(s.st_mode)) {
+ type = '0'; // tar magic: '0' == normal file
+ } else {
+ LOGW("Error: unknown file mode 0%o [%s]", s.st_mode, filepath.string());
+ goto cleanup;
+ }
+ buf[156] = type;
+
+ // [ 157 : 100 ] name of linked file [not implemented]
+
+ // Now go back and calculate the header checksum
+ {
+ uint16_t sum = 0;
+ for (uint8_t* p = (uint8_t*) buf; p < ((uint8_t*)buf) + 512; p++) {
+ sum += *p;
+ }
+
+ // Now write the real checksum value:
+ // [ 148 : 8 ] checksum: 6 octal digits [leading zeroes], NUL, SPC
+ sprintf(buf + 148, "%06o", sum); // the trailing space is already in place
+ }
+
+ // Write the 512-byte tar file header block to the output
+ writer->WriteEntityData(buf, 512);
+
+ // Now write the file data itself, for real files. We honor tar's convention that
+ // only full 512-byte blocks are sent to write().
+ if (!isdir) {
+ off64_t toWrite = s.st_size;
+ while (toWrite > 0) {
+ size_t toRead = (toWrite < BUFSIZE) ? toWrite : BUFSIZE;
+ ssize_t nRead = read(fd, buf, toRead);
+ if (nRead < 0) {
+ err = errno;
+ LOGE("Unable to read file [%s], err=%d (%s)", filepath.string(),
+ err, strerror(err));
+ break;
+ } else if (nRead == 0) {
+ LOGE("EOF but expect %lld more bytes in [%s]", (long long) toWrite,
+ filepath.string());
+ err = EIO;
+ break;
+ }
+
+ // At EOF we might have a short block; NUL-pad that to a 512-byte multiple. This
+ // depends on the OS guarantee that for ordinary files, read() will never return
+ // less than the number of bytes requested.
+ ssize_t partial = (nRead+512) % 512;
+ if (partial > 0) {
+ ssize_t remainder = 512 - partial;
+ memset(buf + nRead, 0, remainder);
+ nRead += remainder;
+ }
+ writer->WriteEntityData(buf, nRead);
+ toWrite -= nRead;
+ }
+ }
+
+cleanup:
+ delete [] buf;
+done:
+ close(fd);
+ return err;
+}
+// end tarfile
+
+
+
#define RESTORE_BUF_SIZE (8*1024)
RestoreHelperBase::RestoreHelperBase()