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Re: [PATCH] error handling: Use TFR() macro where applicable
From: |
Christian Schoenebeck |
Subject: |
Re: [PATCH] error handling: Use TFR() macro where applicable |
Date: |
Mon, 08 Aug 2022 14:52:28 +0200 |
On Montag, 8. August 2022 10:05:56 CEST Markus Armbruster wrote:
> 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.
So far scripts/checkpatch.pl doesn't complain, therefore I used this code
style in QEMU before.
BTW, another exotic function call code style (not being compalained about yet)
in approach:
https://lore.kernel.org/qemu-devel/E1oDQqv-0003d4-Hm@lizzy.crudebyte.com/
> > 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.
For consistency and simplicity, I would define exactly one version (no ifdefs)
of the macro with a different macro name than glibc's TEMP_FAILURE_RETRY(),
and use that QEMU specific macro name in QEMU code everywhere.
As for statement vs. expression: The only advantage of the statement version
is if you'd need __result as an rvalue, which is not needed ATM, right? So I
would go for the expression version (with cast) for now.
The glibc history does not reveal why they chose the statement version.
Best regards,
Christian Schoenebeck
- [PATCH] error handling: Use TFR() macro where applicable, Nikita Ivanov, 2022/08/04
- Re: [PATCH] error handling: Use TFR() macro where applicable, Christian Schoenebeck, 2022/08/05
- Re: [PATCH] error handling: Use TFR() macro where applicable, Marc-André Lureau, 2022/08/05
- Re: [PATCH] error handling: Use TFR() macro where applicable, Peter Maydell, 2022/08/05
- Re: [PATCH] error handling: Use TFR() macro where applicable, Nikita Ivanov, 2022/08/08
- Re: [PATCH] error handling: Use TFR() macro where applicable, Markus Armbruster, 2022/08/08
- Re: [PATCH] error handling: Use TFR() macro where applicable, Nikita Ivanov, 2022/08/08
- Re: [PATCH] error handling: Use TFR() macro where applicable,
Christian Schoenebeck <=
- Re: [PATCH] error handling: Use TFR() macro where applicable, Christian Schoenebeck, 2022/08/08
- Re: [PATCH] error handling: Use TFR() macro where applicable, Markus Armbruster, 2022/08/08
- Re: [PATCH] error handling: Use TFR() macro where applicable, Nikita Ivanov, 2022/08/08
- Re: [PATCH] error handling: Use TFR() macro where applicable, Nikita Ivanov, 2022/08/08
- Re: [PATCH] error handling: Use TFR() macro where applicable, Nikita Ivanov, 2022/08/17
- Re: [PATCH] error handling: Use TFR() macro where applicable, Peter Maydell, 2022/08/17
- Re: [PATCH] error handling: Use TFR() macro where applicable, Nikita Ivanov, 2022/08/17
- Re: [PATCH] error handling: Use TFR() macro where applicable, Peter Maydell, 2022/08/17
- Re: [PATCH] error handling: Use TFR() macro where applicable, Christian Schoenebeck, 2022/08/18
- Re: [PATCH] error handling: Use TFR() macro where applicable, Peter Maydell, 2022/08/18