Re: [fsverity-utils PATCH 3/4] programs/utils: add full_pwrite() and preallocate_file()

[Victor Hsieh <victorhsieh@google.com>]

On Thu, Jun 3, 2021 at 1:00 PM Eric Biggers <ebiggers@kernel.org> wrote:
>
> From: Eric Biggers <ebiggers@google.com>
>
> These helper functions will be used by the implementation of the
> --out-merkle-tree option for 'fsverity digest' and 'fsverity sign'.
>
> Signed-off-by: Eric Biggers <ebiggers@google.com>
> ---
>  programs/utils.c | 59 ++++++++++++++++++++++++++++++++++++++++++++++++
>  programs/utils.h |  3 +++
>  2 files changed, 62 insertions(+)
>
> diff --git a/programs/utils.c b/programs/utils.c
> index ce19b57..116eb95 100644
> --- a/programs/utils.c
> +++ b/programs/utils.c
> @@ -13,10 +13,14 @@
>
>  #include <errno.h>
>  #include <fcntl.h>
> +#include <inttypes.h>
>  #include <limits.h>
>  #include <stdarg.h>
>  #include <sys/stat.h>
>  #include <unistd.h>
> +#ifdef _WIN32
> +#  include <windows.h>
> +#endif
>
>  /* ========== Memory allocation ========== */
>
> @@ -126,6 +130,26 @@ bool get_file_size(struct filedes *file, u64 *size_ret)
>         return true;
>  }
>
> +bool preallocate_file(struct filedes *file, u64 size)
> +{
> +       int res;
> +
> +       if (size == 0)
> +               return true;
> +#ifdef _WIN32
> +       /* Not exactly the same as posix_fallocate(), but good enough... */
> +       res = _chsize_s(file->fd, size);
> +#else
> +       res = posix_fallocate(file->fd, 0, size);
> +#endif
> +       if (res != 0) {
> +               error_msg_errno("preallocating %" PRIu64 "-byte file '%s'",
> +                               size, file->name);
> +               return false;
> +       }
> +       return true;
> +}
> +
>  bool full_read(struct filedes *file, void *buf, size_t count)
>  {
>         while (count) {
> @@ -160,6 +184,41 @@ bool full_write(struct filedes *file, const void *buf, size_t count)
>         return true;
>  }
>
> +static int raw_pwrite(int fd, const void *buf, int count, u64 offset)
> +{
> +#ifdef _WIN32
> +       HANDLE h = (HANDLE)_get_osfhandle(fd);
> +       OVERLAPPED pos = { .Offset = offset, .OffsetHigh = offset >> 32 };
> +       DWORD written = 0;
> +
> +       /* Not exactly the same as pwrite(), but good enough... */
> +       if (!WriteFile(h, buf, count, &written, &pos)) {
> +               errno = EIO;
> +               return -1;
> +       }
> +       return written;
> +#else
> +       return pwrite(fd, buf, count, offset);
> +#endif
> +}
> +
> +bool full_pwrite(struct filedes *file, const void *buf, size_t count,
> +                u64 offset)
> +{
> +       while (count) {
> +               int n = raw_pwrite(file->fd, buf, min(count, INT_MAX), offset);
> +
> +               if (n < 0) {
> +                       error_msg_errno("writing to '%s'", file->name);
> +                       return false;
> +               }
> +               buf += n;
I think this pointer arithmetic is not portable?  Consider changing
the type of buf to "const char*".

> +               count -= n;
> +               offset += n;
> +       }
> +       return true;
> +}
> +
>  bool filedes_close(struct filedes *file)
>  {
>         int res;
> diff --git a/programs/utils.h b/programs/utils.h
> index ab5005f..9a5c97a 100644
> --- a/programs/utils.h
> +++ b/programs/utils.h
> @@ -40,8 +40,11 @@ struct filedes {
>
>  bool open_file(struct filedes *file, const char *filename, int flags, int mode);
>  bool get_file_size(struct filedes *file, u64 *size_ret);
> +bool preallocate_file(struct filedes *file, u64 size);
>  bool full_read(struct filedes *file, void *buf, size_t count);
>  bool full_write(struct filedes *file, const void *buf, size_t count);
> +bool full_pwrite(struct filedes *file, const void *buf, size_t count,
> +                u64 offset);
>  bool filedes_close(struct filedes *file);
>  int read_callback(void *file, void *buf, size_t count);
>
> --
> 2.31.1
>