fastboot driver: add fetch command in driver

The `fastboot fetch` command is a wrapper around
the fetch protocol. It:

- getvar max-fetch-size
- get the size of the partition
- read the data by chunks, chunk size = max-fetch-size.

The name of the partition is passed directly to the device
(with the usual has-slot magic for flashing etc.) If we support
fetching partitions other than vendor_boot in the future, no change
in the driver is needed.

Bug: 173654501
Test: manual

Change-Id: Ie576eea668234df236b096a372e65c5e91c1e48c

fastboot/device/commands.cpp

@@ -712,13 +712,20 @@ class PartitionFetcher {
     // If successfully opened, ret_ is left untouched. Otherwise, ret_ is set to the value
     // that FetchHandler should return.
     bool Open() {
-        partition_name_ = args_->at(1);
-        if (partition_name_ != "vendor_boot") {
-            ret_ = device_->WriteFail("Fetch is only allowed on vendor_boot");
+        if (args_->size() < 2) {
+            ret_ = device_->WriteFail("Missing partition arg");
             return false;
         }
 
-        if (!OpenPartition(device_, partition_name_, &handle_)) {
+        partition_name_ = args_->at(1);
+        if (std::find(kAllowedPartitions.begin(), kAllowedPartitions.end(), partition_name_) ==
+            kAllowedPartitions.end()) {
+            ret_ = device_->WriteFail("Fetch is only allowed on [" +
+                                      android::base::Join(kAllowedPartitions, ", ") + "]");
+            return false;
+        }
+
+        if (!OpenPartition(device_, partition_name_, &handle_, true /* read */)) {
             ret_ = device_->WriteFail(
                     android::base::StringPrintf("Cannot open %s", partition_name_.c_str()));
             return false;
@@ -826,6 +833,12 @@ class PartitionFetcher {
                 start_offset_, total_size_to_read_));
     }
 
+    static constexpr std::array<const char*, 3> kAllowedPartitions{
+            "vendor_boot",
+            "vendor_boot_a",
+            "vendor_boot_b",
+    };
+
     FastbootDevice* device_;
     const std::vector<std::string>* args_ = nullptr;
     std::string partition_name_;

fastboot/fastboot.cpp

@@ -77,11 +77,13 @@
 #include "usb.h"
 #include "util.h"
 
+using android::base::borrowed_fd;
 using android::base::ReadFully;
 using android::base::Split;
 using android::base::Trim;
 using android::base::unique_fd;
 using namespace std::string_literals;
+using namespace std::placeholders;
 
 static const char* serial = nullptr;
 
@@ -414,6 +416,7 @@ static int show_help() {
             " snapshot-update merge      On devices that support snapshot-based updates, finish\n"
             "                            an in-progress update if it is in the \"merging\"\n"
             "                            phase.\n"
+            " fetch PARTITION            Fetch a partition image from the device."
             "\n"
             "boot image:\n"
             " boot KERNEL [RAMDISK [SECOND]]\n"
@@ -466,7 +469,7 @@ static int show_help() {
             " --version                  Display version.\n"
             " --help, -h                 Show this message.\n"
         );
-    // clang-format off
+    // clang-format on
     return 0;
 }
 
@@ -851,24 +854,23 @@ static struct sparse_file** load_sparse_files(int fd, int64_t max_size) {
     return out_s;
 }
 
-static int64_t get_target_sparse_limit() {
-    std::string max_download_size;
-    if (fb->GetVar("max-download-size", &max_download_size) != fastboot::SUCCESS ||
-        max_download_size.empty()) {
-        verbose("target didn't report max-download-size");
+static uint64_t get_uint_var(const char* var_name) {
+    std::string value_str;
+    if (fb->GetVar(var_name, &value_str) != fastboot::SUCCESS || value_str.empty()) {
+        verbose("target didn't report %s", var_name);
         return 0;
     }
 
     // Some bootloaders (angler, for example) send spurious whitespace too.
-    max_download_size = android::base::Trim(max_download_size);
+    value_str = android::base::Trim(value_str);
 
-    uint64_t limit;
-    if (!android::base::ParseUint(max_download_size, &limit)) {
-        fprintf(stderr, "couldn't parse max-download-size '%s'\n", max_download_size.c_str());
+    uint64_t value;
+    if (!android::base::ParseUint(value_str, &value)) {
+        fprintf(stderr, "couldn't parse %s '%s'\n", var_name, value_str.c_str());
         return 0;
     }
-    if (limit > 0) verbose("target reported max download size of %" PRId64 " bytes", limit);
-    return limit;
+    if (value > 0) verbose("target reported %s of %" PRId64 " bytes", var_name, value);
+    return value;
 }
 
 static int64_t get_sparse_limit(int64_t size) {
@@ -877,7 +879,7 @@ static int64_t get_sparse_limit(int64_t size) {
         // Unlimited, so see what the target device's limit is.
         // TODO: shouldn't we apply this limit even if you've used -S?
         if (target_sparse_limit == -1) {
-            target_sparse_limit = get_target_sparse_limit();
+            target_sparse_limit = static_cast<int64_t>(get_uint_var("max-download-size"));
         }
         if (target_sparse_limit > 0) {
             limit = target_sparse_limit;
@@ -1011,21 +1013,28 @@ static std::string fb_fix_numeric_var(std::string var) {
     return var;
 }
 
-static void copy_boot_avb_footer(const std::string& partition, struct fastboot_buffer* buf) {
-    if (buf->sz < AVB_FOOTER_SIZE) {
-        return;
-    }
-
+static uint64_t get_partition_size(const std::string& partition) {
     std::string partition_size_str;
     if (fb->GetVar("partition-size:" + partition, &partition_size_str) != fastboot::SUCCESS) {
         die("cannot get partition size for %s", partition.c_str());
     }
 
     partition_size_str = fb_fix_numeric_var(partition_size_str);
-    int64_t partition_size;
-    if (!android::base::ParseInt(partition_size_str, &partition_size)) {
+    uint64_t partition_size;
+    if (!android::base::ParseUint(partition_size_str, &partition_size)) {
         die("Couldn't parse partition size '%s'.", partition_size_str.c_str());
     }
+    return partition_size;
+}
+
+static void copy_boot_avb_footer(const std::string& partition, struct fastboot_buffer* buf) {
+    if (buf->sz < AVB_FOOTER_SIZE) {
+        return;
+    }
+
+    // If overflows and negative, it should be < buf->sz.
+    int64_t partition_size = static_cast<int64_t>(get_partition_size(partition));
+
     if (partition_size == buf->sz) {
         return;
     }
@@ -1245,6 +1254,38 @@ static bool is_retrofit_device() {
     return android::base::StartsWith(value, "system_");
 }
 
+// Fetch a partition from the device to a given fd. This is a wrapper over FetchToFd to fetch
+// the full image.
+static uint64_t fetch_partition(const std::string& partition, borrowed_fd fd) {
+    uint64_t fetch_size = get_uint_var(FB_VAR_MAX_FETCH_SIZE);
+    if (fetch_size == 0) {
+        die("Unable to get %s. Device does not support fetch command.", FB_VAR_MAX_FETCH_SIZE);
+    }
+    uint64_t partition_size = get_partition_size(partition);
+    if (partition_size <= 0) {
+        die("Invalid partition size for partition %s: %" PRId64, partition.c_str(), partition_size);
+    }
+
+    uint64_t offset = 0;
+    while (offset < partition_size) {
+        uint64_t chunk_size = std::min(fetch_size, partition_size - offset);
+        if (fb->FetchToFd(partition, fd, offset, chunk_size) != fastboot::RetCode::SUCCESS) {
+            die("Unable to fetch %s (offset=%" PRIx64 ", size=%" PRIx64 ")", partition.c_str(),
+                offset, chunk_size);
+        }
+        offset += chunk_size;
+    }
+    return partition_size;
+}
+
+static void do_fetch(const std::string& partition, const std::string& slot_override,
+                     const std::string& outfile) {
+    unique_fd fd(TEMP_FAILURE_RETRY(
+            open(outfile.c_str(), O_WRONLY | O_CREAT | O_TRUNC | O_CLOEXEC | O_BINARY, 0644)));
+    auto fetch = std::bind(fetch_partition, _1, borrowed_fd(fd));
+    do_for_partitions(partition, slot_override, fetch, false /* force slot */);
+}
+
 static void do_flash(const char* pname, const char* fname) {
     struct fastboot_buffer buf;
 
@@ -2167,6 +2208,10 @@ int FastBootTool::Main(int argc, char* argv[]) {
                 syntax_error("expected: snapshot-update [cancel|merge]");
             }
             fb->SnapshotUpdateCommand(arg);
+        } else if (command == FB_CMD_FETCH) {
+            std::string partition = next_arg(&args);
+            std::string outfile = next_arg(&args);
+            do_fetch(partition, slot_override, outfile);
         } else {
             syntax_error("unknown command %s", command.c_str());
         }

fastboot/fastboot_driver.cpp

@@ -30,6 +30,7 @@
 
 #include <errno.h>
 #include <fcntl.h>
+#include <inttypes.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -42,6 +43,7 @@
 
 #include <android-base/file.h>
 #include <android-base/mapped_file.h>
+#include <android-base/parseint.h>
 #include <android-base/stringprintf.h>
 #include <android-base/strings.h>
 #include <android-base/unique_fd.h>
@@ -357,6 +359,29 @@ RetCode FastBootDriver::UploadInner(const std::string& outfile, std::string* res
     return ret;
 }
 
+RetCode FastBootDriver::FetchToFd(const std::string& partition, android::base::borrowed_fd fd,
+                                  int64_t offset, int64_t size, std::string* response,
+                                  std::vector<std::string>* info) {
+    prolog_(android::base::StringPrintf("Fetching %s (offset=%" PRIx64 ", size=%" PRIx64 ")",
+                                        partition.c_str(), offset, size));
+    std::string cmd = FB_CMD_FETCH ":" + partition;
+    if (offset >= 0) {
+        cmd += android::base::StringPrintf(":0x%08" PRIx64, offset);
+        if (size >= 0) {
+            cmd += android::base::StringPrintf(":0x%08" PRIx64, size);
+        }
+    }
+    RetCode ret = RunAndReadBuffer(cmd, response, info, [&](const char* data, uint64_t size) {
+        if (!android::base::WriteFully(fd, data, size)) {
+            error_ = android::base::StringPrintf("Cannot write: %s", strerror(errno));
+            return IO_ERROR;
+        }
+        return SUCCESS;
+    });
+    epilog_(ret);
+    return ret;
+}
+
 // Helpers
 void FastBootDriver::SetInfoCallback(std::function<void(const std::string&)> info) {
     info_ = info;

fastboot/fastboot_driver.h

@@ -34,6 +34,7 @@
 
 #include <android-base/logging.h>
 #include <android-base/stringprintf.h>
+#include <android-base/unique_fd.h>
 #include <bootimg.h>
 #include <inttypes.h>
 #include <sparse/sparse.h>
@@ -106,6 +107,9 @@ class FastBootDriver {
                    std::vector<std::string>* info = nullptr);
     RetCode SnapshotUpdateCommand(const std::string& command, std::string* response = nullptr,
                                   std::vector<std::string>* info = nullptr);
+    RetCode FetchToFd(const std::string& partition, android::base::borrowed_fd fd,
+                      int64_t offset = -1, int64_t size = -1, std::string* response = nullptr,
+                      std::vector<std::string>* info = nullptr);
 
     /* HIGHER LEVEL COMMANDS -- Composed of the commands above */
     RetCode FlashPartition(const std::string& partition, const std::vector<char>& data);