zircon/system/ulib/zbitl/fd.cc

// Copyright 2020 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include <errno.h>
#include <lib/cksum.h>
#include <lib/zbitl/fd.h>
#include <sys/stat.h>
#include <unistd.h>

#include <memory>
#include <new>

namespace zbitl {
namespace {

constexpr size_t kBufferSize = 8192;

using error_type = StorageTraits<fbl::unique_fd>::error_type;

}  // namespace

fitx::result<error_type, uint32_t> StorageTraits<fbl::unique_fd>::Capacity(
    const fbl::unique_fd& fd) {
  struct stat st;
  if (fstat(fd.get(), &st) < 0) {
    return fitx::error{errno};
  }
  auto size = std::min(static_cast<off_t>(std::numeric_limits<uint32_t>::max()), st.st_size);
  return fitx::ok(static_cast<uint32_t>(size));
}

fitx::result<error_type> StorageTraits<fbl::unique_fd>::EnsureCapacity(fbl::unique_fd& fd,
                                                                       uint32_t capacity_bytes) {
  auto current = Capacity(fd);
  if (current.is_error()) {
    return current.take_error();
  } else if (current.value() >= capacity_bytes) {
    return fitx::ok();  // Current capacity is sufficient.
  }
  // Write a single byte to reserve enough space for the new capacity.
  if (ssize_t n = pwrite(fd.get(), "", 1, capacity_bytes - 1); n < 0) {
    return fitx::error{errno};
  }
  return fitx::ok();
}

fitx::result<error_type> StorageTraits<fbl::unique_fd>::Read(const fbl::unique_fd& fd, off_t offset,
                                                             void* buffer, uint32_t length) {
  auto p = static_cast<std::byte*>(buffer);
  while (length > 0) {
    ssize_t n = pread(fd.get(), p, length, offset);
    if (n < 0) {
      return fitx::error{errno};
    }
    if (n == 0) {
      return fitx::error{ESPIPE};
    }
    ZX_DEBUG_ASSERT(static_cast<size_t>(n) <= length);
    length -= static_cast<uint32_t>(n);
    p += n;
    offset += n;
  }
  return fitx::ok();
}

fitx::result<error_type> StorageTraits<fbl::unique_fd>::DoRead(const fbl::unique_fd& fd,
                                                               off_t offset, uint32_t length,
                                                               bool (*cb)(void*, ByteView),
                                                               void* arg) {
  if (length == 0) {
    cb(arg, {});
    return fitx::ok();
  }

  // This always copies, when mmap'ing might be better for large sizes.  But
  // address space is cheap, so users concerned with large sizes can just mmap
  // the whole ZBI in and use View<std::span> instead.
  auto size = [&]() { return std::min(static_cast<size_t>(length), kBufferSize); };
  std::unique_ptr<std::byte[]> buf{new std::byte[size()]};

  while (length > 0) {
    ssize_t n = pread(fd.get(), buf.get(), size(), offset);
    if (n < 0) {
      return fitx::error{errno};
    }
    if (n == 0) {
      return fitx::error{ESPIPE};
    }
    ZX_ASSERT(static_cast<size_t>(n) <= kBufferSize);
    if (!cb(arg, {buf.get(), static_cast<size_t>(n)})) {
      break;
    }
    offset += n;
    length -= static_cast<uint32_t>(n);
  }

  return fitx::ok();
}

fitx::result<error_type> StorageTraits<fbl::unique_fd>::Write(const fbl::unique_fd& fd,
                                                              uint32_t offset, ByteView data) {
  while (!data.empty()) {
    ssize_t n = pwrite(fd.get(), data.data(), data.size(), offset);
    if (n < 0) {
      return fitx::error{errno};
    }
    ZX_ASSERT(static_cast<size_t>(n) <= data.size());
    offset += static_cast<uint32_t>(n);
    data = data.subspan(static_cast<size_t>(n));
  }
  return fitx::ok();
}

}  // namespace zbitl