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Re: [PATCH 2/7] ios: Pass offset to low-level macros.

From: Eric Blake
Subject: Re: [PATCH 2/7] ios: Pass offset to low-level macros.
Date: Sat, 29 Feb 2020 07:26:03 -0600
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0

On 2/29/20 5:12 AM, Eric Blake wrote:
This patch should have no semantic change, although it might have a
slight pessimization in performance which will be cleaned up in later

(IOS_READ_INTO_CHARRAY_9BYTES): Add parameter (unused until next
(ios_write_int_fast): Add parameter.
(ios_read_int_common, ios_read_int, ios_read_uint)
(ios_write_int_common, ios_write_int, ios_write_uint): Adjust
  ChangeLog |  15 +++
  src/ios.c | 395 +++++++++++++++++++++++++++---------------------------
  2 files changed, 213 insertions(+), 197 deletions(-)

+++ b/src/ios.c
@@ -32,7 +32,7 @@

  #define STREQ(a, b) (strcmp (a, b) == 0)

-#define IOS_GET_C_ERR_CHCK(c, io)               \
+#define IOS_GET_C_ERR_CHCK(c, io, off)         \
    {                                             \
    int ret = io->dev_if->get_c ((io)->dev);   \

Just noticing: We're inconsistent on whether the 'io' argument to this macro is allowed to be an arbitrary expression. Fortunately, none of the callers pass a complex expression, but the correct spelling for arbitrary syntax would be:

int ret = (io)->dev_if->get_c ((io)->dev); \

yet that still would result in multiple side effects; so even more reusable would be:

ios io_ = (io); \
int ret = io_->dev_if->get_c (io_->dev); \

Or, we can declare that this macro is not intended to be reusable outside this file, and could spell it:

int ret = io->dev_if->get_c (io->dev); \

or go one step further and declare that it is only to be run inside a function where 'io' is already in scope, and not pass in an io argument to the macro.

I don't have any strong preferences, but am happy to tweak this and subsequent patches to match any style that someone expresses a preference for.

Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org

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