Improved libdm and dmctl to handle very large numbers of extents

Enables performance testing with very large numbers of dm-linear devices

Test: Can create device with 16384 extents, and can get its table
Bug: 123261135
Change-Id: I0e78a659eb7616e4db6a8276031e25a0d84f52ba

fs_mgr/libdm/dm.cpp

@@ -299,24 +299,25 @@ bool DeviceMapper::GetTableInfo(const std::string& name, std::vector<TargetInfo>
 // private methods of DeviceMapper
 bool DeviceMapper::GetTable(const std::string& name, uint32_t flags,
                             std::vector<TargetInfo>* table) {
-    char buffer[4096];
-    struct dm_ioctl* io = reinterpret_cast<struct dm_ioctl*>(buffer);
+    std::vector<char> buffer;
+    struct dm_ioctl* io = nullptr;
 
-    InitIo(io, name);
-    io->data_size = sizeof(buffer);
-    io->data_start = sizeof(*io);
-    io->flags = flags;
-    if (ioctl(fd_, DM_TABLE_STATUS, io) < 0) {
-        PLOG(ERROR) << "DM_TABLE_STATUS failed for " << name;
-        return false;
-    }
-    if (io->flags & DM_BUFFER_FULL_FLAG) {
-        PLOG(ERROR) << "DM_TABLE_STATUS result for " << name << " was too large";
-        return false;
+    for (buffer.resize(4096);; buffer.resize(buffer.size() * 2)) {
+        io = reinterpret_cast<struct dm_ioctl*>(&buffer[0]);
+
+        InitIo(io, name);
+        io->data_size = buffer.size();
+        io->data_start = sizeof(*io);
+        io->flags = flags;
+        if (ioctl(fd_, DM_TABLE_STATUS, io) < 0) {
+            PLOG(ERROR) << "DM_TABLE_STATUS failed for " << name;
+            return false;
+        }
+        if (!(io->flags & DM_BUFFER_FULL_FLAG)) break;
     }
 
     uint32_t cursor = io->data_start;
-    uint32_t data_end = std::min(io->data_size, uint32_t(sizeof(buffer)));
+    uint32_t data_end = std::min(io->data_size, uint32_t(buffer.size()));
     for (uint32_t i = 0; i < io->target_count; i++) {
         if (cursor + sizeof(struct dm_target_spec) > data_end) {
             break;
@@ -324,14 +325,14 @@ bool DeviceMapper::GetTable(const std::string& name, uint32_t flags,
         // After each dm_target_spec is a status string. spec->next is an
         // offset from |io->data_start|, and we clamp it to the size of our
         // buffer.
-        struct dm_target_spec* spec = reinterpret_cast<struct dm_target_spec*>(buffer + cursor);
+        struct dm_target_spec* spec = reinterpret_cast<struct dm_target_spec*>(&buffer[cursor]);
         uint32_t data_offset = cursor + sizeof(dm_target_spec);
         uint32_t next_cursor = std::min(io->data_start + spec->next, data_end);
 
         std::string data;
         if (next_cursor > data_offset) {
             // Note: we use c_str() to eliminate any extra trailing 0s.
-            data = std::string(buffer + data_offset, next_cursor - data_offset).c_str();
+            data = std::string(&buffer[data_offset], next_cursor - data_offset).c_str();
         }
         table->emplace_back(*spec, data);
         cursor = next_cursor;

fs_mgr/tools/dmctl.cpp

@@ -27,6 +27,7 @@
 #include <android-base/unique_fd.h>
 #include <libdm/dm.h>
 
+#include <fstream>
 #include <functional>
 #include <iomanip>
 #include <ios>
@@ -50,6 +51,7 @@ using DmBlockDevice = ::android::dm::DeviceMapper::DmBlockDevice;
 
 static int Usage(void) {
     std::cerr << "usage: dmctl <command> [command options]" << std::endl;
+    std::cerr << "       dmctl -f file" << std::endl;
     std::cerr << "commands:" << std::endl;
     std::cerr << "  create <dm-name> [-ro] <targets...>" << std::endl;
     std::cerr << "  delete <dm-name>" << std::endl;
@@ -58,6 +60,8 @@ static int Usage(void) {
     std::cerr << "  table <dm-name>" << std::endl;
     std::cerr << "  help" << std::endl;
     std::cerr << std::endl;
+    std::cerr << "-f file reads command and all parameters from named file" << std::endl;
+    std::cerr << std::endl;
     std::cerr << "Target syntax:" << std::endl;
     std::cerr << "  <target_type> <start_sector> <num_sectors> [target_data]" << std::endl;
     return -EINVAL;
@@ -340,12 +344,40 @@ static std::map<std::string, std::function<int(int, char**)>> cmdmap = {
         // clang-format on
 };
 
+static bool ReadFile(const char* filename, std::vector<std::string>* args,
+                     std::vector<char*>* arg_ptrs) {
+    std::ifstream file(filename);
+    if (!file) return false;
+
+    std::string arg;
+    while (file >> arg) args->push_back(arg);
+
+    for (auto const& i : *args) arg_ptrs->push_back(const_cast<char*>(i.c_str()));
+    return true;
+}
+
 int main(int argc, char** argv) {
     android::base::InitLogging(argv, &android::base::StderrLogger);
     if (argc < 2) {
         return Usage();
     }
 
+    std::vector<std::string> args;
+    std::vector<char*> arg_ptrs;
+    if (std::string("-f") == argv[1]) {
+        if (argc != 3) {
+            return Usage();
+        }
+
+        args.push_back(argv[0]);
+        if (!ReadFile(argv[2], &args, &arg_ptrs)) {
+            return Usage();
+        }
+
+        argc = arg_ptrs.size();
+        argv = &arg_ptrs[0];
+    }
+
     for (const auto& cmd : cmdmap) {
         if (cmd.first == argv[1]) {
             return cmd.second(argc - 2, argv + 2);