Re: What's cooking in git.git (Apr 2012, #06; Sun, 15)
- From
Nguyen Thai Ngoc Duy <pclouds@gmail.com>
- Date
- Apr 19, 2012, 13:18 UTC
- Message-ID
- <CACsJy8DDLmKkBMW_P8RyGTRw=i6OKWZNf-SHoGkVWnJgfK7cVQ@mail.gmail.com>
- In-Reply-To
- <CABPQNSZ6VdyoLcVUUJ4z5A2A7KGP8qBZAkzdx8zAtAs2mZN25w@mail.gmail.com>
On Thu, Apr 19, 2012 at 7:58 PM, Erik Faye-Lund <kusmabite@gmail.com> wrote:
Show 6 quoted lines
> This approach has the problem that file-operations apart from pread > might (at least in theory) modify the position. To prevent that, we'd > either need to use the same locking-mechanism as the CRT use, or use > ReadFile with an OVERLAPPED struct, which allows us specify the offset > explicitly. The latter seems better to me, and should look something > like this (note: untested):
Yeah. I read about ReadFile [1] but dismissed it when I got to async i/o mode. Reading again, sync i/o ReadFile with OVERLAPPED struct should work fine. It's not clear though if file offset is changed (pread man page says it does not change).
Also this approach deals with Windows only. There's still another NO_PREAD user, HP-UX something, and NO_PREAD comment mentions cygwin before v1.5.22. I personally don't care, just wanted to point out.
[1] http://msdn.microsoft.com/en-us/library/windows/desktop/aa365467(v=vs.85).aspx
Show 67 quoted lines
> diff --git a/Makefile b/Makefile
> index 2626216..31a5621 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -1153,7 +1153,6 @@ endif
> ifeq ($(uname_S),Windows)
> GIT_VERSION := $(GIT_VERSION).MSVC
> pathsep = ;
> - NO_PREAD = YesPlease
> NEEDS_CRYPTO_WITH_SSL = YesPlease
> NO_LIBGEN_H = YesPlease
> NO_SYS_POLL_H = YesPlease
> @@ -1250,7 +1249,6 @@ ifeq ($(uname_S),Minix)
> endif
> ifneq (,$(findstring MINGW,$(uname_S)))
> pathsep = ;
> - NO_PREAD = YesPlease
> NEEDS_CRYPTO_WITH_SSL = YesPlease
> NO_LIBGEN_H = YesPlease
> NO_SYS_POLL_H = YesPlease
> diff --git a/compat/mingw.c b/compat/mingw.c
> index 309fa1d..63783db 100644
> --- a/compat/mingw.c
> +++ b/compat/mingw.c
> @@ -617,6 +617,28 @@ static inline void time_t_to_filetime(time_t t,
> FILETIME *ft)
> ft->dwHighDateTime = winTime >> 32;
> }
>
> +ssize_t mingw_pread(int fd, void *buf, size_t size, off_t offset)
> +{
> + OVERLAPPED overlapped = { 0 };
> + DWORD ret;
> +
> + HANDLE fh = (HANDLE)_get_osfhandle(fd);
> + if (fh == INVALID_HANDLE_VALUE) {
> + errno = EBADF;
> + return -1;
> + }
> +
> + overlapped.Offset = (DWORD)offset;
> + overlapped.OffsetHigh = (DWORD)(offset >> 32);
> +
> + if (!ReadFile(fh, buf, size, &ret, &overlapped)) {
> + errno = err_win_to_posix(GetLastError());
> + return -1;
> + }
> +
> + return ret;
> +}
> +
> int mingw_utime (const char *file_name, const struct utimbuf *times)
> {
> FILETIME mft, aft;
> diff --git a/compat/mingw.h b/compat/mingw.h
> index c7b2cec..da47302 100644
> --- a/compat/mingw.h
> +++ b/compat/mingw.h
> @@ -285,6 +285,9 @@ int mingw_fstat(int fd, struct stat *buf);
> #define _stati64(x,y) mingw_stat(x,y)
> #endif
>
> +ssize_t mingw_pread(int fd, void *buf, size_t count, off_t offset);
> +#define pread mingw_pread
> +
> int mingw_utime(const char *file_name, const struct utimbuf *times);
> #define utime mingw_utime-- Duy