Re: [PATCH] error handling: Use TFR() macro where applicable

[Markus Armbruster]

Nikita Ivanov <nivanov@cloudlinux.com> writes:

> Summing up the discussion above, I suggest the following patch for TFR()
> macro refactoring. (The patch is sequential to the first one I introduced
> in the start of the discussion).
>
>>From 6318bee052900aa93bba6620b53c7cb2290e5001 Mon Sep 17 00:00:00 2001
> From: Nikita Ivanov <nivanov@cloudlinux.com>
> Date: Mon, 8 Aug 2022 09:30:34 +0300
> Subject: [PATCH] Refactoring: rename TFR() to TEMP_FAILURE_RETRY()
>
> glibc's unistd.h header provides the same macro with the
> subtle difference in type casting. Adjust macro name to the
> common standard and define conditionally.
>
> Signed-off-by: Nikita Ivanov <nivanov@cloudlinux.com>
> ---
>  chardev/char-fd.c      |  2 +-
>  chardev/char-pipe.c    | 12 +++++++++---
>  hw/9pfs/9p-local.c     |  6 ++++--
>  include/qemu/osdep.h   |  6 ++++--
>  net/l2tpv3.c           |  8 +++++---
>  net/tap-linux.c        |  2 +-
>  net/tap.c              | 10 ++++++----
>  os-posix.c             |  2 +-
>  qga/commands-posix.c   |  2 +-
>  tests/qtest/libqtest.c |  2 +-
>  util/main-loop.c       |  2 +-
>  util/osdep.c           |  2 +-
>  12 files changed, 35 insertions(+), 21 deletions(-)
>
> diff --git a/chardev/char-fd.c b/chardev/char-fd.c
> index cf78454841..7f5ed9aba3 100644
> --- a/chardev/char-fd.c
> +++ b/chardev/char-fd.c
> @@ -198,7 +198,7 @@ int qmp_chardev_open_file_source(char *src, int flags,
> Error **errp)
>  {
>      int fd = -1;
>
> -    TFR(fd = qemu_open_old(src, flags, 0666));
> +    TEMP_FAILURE_RETRY(fd = qemu_open_old(src, flags, 0666));
>      if (fd == -1) {
>          error_setg_file_open(errp, errno, src);
>      }
> diff --git a/chardev/char-pipe.c b/chardev/char-pipe.c
> index 66d3b85091..aed97e306b 100644
> --- a/chardev/char-pipe.c
> +++ b/chardev/char-pipe.c
> @@ -131,8 +131,12 @@ static void qemu_chr_open_pipe(Chardev *chr,
>
>      filename_in = g_strdup_printf("%s.in", filename);
>      filename_out = g_strdup_printf("%s.out", filename);
> -    TFR(fd_in = qemu_open_old(filename_in, O_RDWR | O_BINARY));
> -    TFR(fd_out = qemu_open_old(filename_out, O_RDWR | O_BINARY));
> +    TEMP_FAILURE_RETRY(
> +        fd_in = qemu_open_old(filename_in, O_RDWR | O_BINARY)
> +    );
> +    TEMP_FAILURE_RETRY(
> +        fd_out = qemu_open_old(filename_out, O_RDWR | O_BINARY)
> +    );

Style question: do we want the ");" on its own line?  I think we
generally don't do that for function and function-like macro calls.

>      g_free(filename_in);
>      g_free(filename_out);
>      if (fd_in < 0 || fd_out < 0) {
> @@ -142,7 +146,9 @@ static void qemu_chr_open_pipe(Chardev *chr,
>          if (fd_out >= 0) {
>              close(fd_out);
>          }
> -        TFR(fd_in = fd_out = qemu_open_old(filename, O_RDWR | O_BINARY));
> +        TEMP_FAILURE_RETRY(
> +            fd_in = fd_out = qemu_open_old(filename, O_RDWR | O_BINARY)
> +        );
>          if (fd_in < 0) {
>              error_setg_file_open(errp, errno, filename);
>              return;
> diff --git a/hw/9pfs/9p-local.c b/hw/9pfs/9p-local.c
> index c90ab947ba..e803c05d0c 100644
> --- a/hw/9pfs/9p-local.c
> +++ b/hw/9pfs/9p-local.c
> @@ -470,7 +470,7 @@ static ssize_t local_readlink(FsContext *fs_ctx,
> V9fsPath *fs_path,
>          if (fd == -1) {
>              return -1;
>          }
> -        TFR(tsize = read(fd, (void *)buf, bufsz));
> +        TEMP_FAILURE_RETRY(tsize = read(fd, (void *)buf, bufsz));
>          close_preserve_errno(fd);
>      } else if ((fs_ctx->export_flags & V9FS_SM_PASSTHROUGH) ||
>                 (fs_ctx->export_flags & V9FS_SM_NONE)) {
> @@ -906,7 +906,9 @@ static int local_symlink(FsContext *fs_ctx, const char
> *oldpath,
>          }
>          /* Write the oldpath (target) to the file. */
>          oldpath_size = strlen(oldpath);
> -        TFR(write_size = write(fd, (void *)oldpath, oldpath_size));
> +        TEMP_FAILURE_RETRY(
> +            write_size = write(fd, (void *)oldpath, oldpath_size)
> +        );
>          close_preserve_errno(fd);
>
>          if (write_size != oldpath_size) {
> diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
> index b1c161c035..55f2927d8b 100644
> --- a/include/qemu/osdep.h
> +++ b/include/qemu/osdep.h
> @@ -242,8 +242,10 @@ void QEMU_ERROR("code path is reachable")
>  #if !defined(ESHUTDOWN)
>  #define ESHUTDOWN 4099
>  #endif
> -
> -#define TFR(expr) do { if ((expr) != -1) break; } while (errno == EINTR)
> +#if !defined(TEMP_FAILURE_RETRY)
> +#define TEMP_FAILURE_RETRY(expr) \
> +    do { if ((expr) != -1) break; } while (errno == EINTR)
> +#endif

GLibc's version is

   # define TEMP_FAILURE_RETRY(expression) \
     (__extension__                                                           \
       ({ long int __result;                                                  \
          do __result = (long int) (expression);                                
      \
          while (__result == -1L && errno == EINTR);                          \
          __result; }))

The difference isn't just "type casting", it's also statement
vs. expression.

Is it a good idea to have the macro expand into a statement on some
hosts, and into an expression on others?  Sure, CI should catch any uses
as expression, but delaying compile errors to CI wastes developer time.

>
>  /* time_t may be either 32 or 64 bits depending on the host OS, and
>   * can be either signed or unsigned, so we can't just hardcode a

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