Re: [Qemu-devel] [PATCH v3] avoid compilation warning/errors on up to date compilers/glibc

[Anthony Liguori <anthony@codemonkey.ws>]

Jean-Christophe Dubois wrote:
> Some system calls are now requiring to have their return value checked.
>
> Without this a warning is emitted and in the case a qemu an error is
> triggered as qemu is considering warnings as errors.
>
> For example:
>
> block/cow.c: In function ‘cow_create’:
> block/cow.c:251: error: ignoring return value of ‘write’, declared with
> attribute warn_unused_result
> block/cow.c:253: error: ignoring return value of ‘ftruncate’, declared
> with attribute warn_unused_result
>
> This is an attempt at removing all these warnings to allow a clean
> compilation with up to date compilers/distributions.
>
> The second version fixes an error detected by Stuart Brady as well
> as some coding style issues. Note however that some of the
> modified files don't follow the qemu coding style (using tabs
> instead of spaces).
>
> The Third version add one ftruncate() system call error handling that
> was missing from V2 (in block/vvfat.c).
>
> Signed-off-by: Jean-Christophe DUBOIS <jcd@tribudubois.net>
>
> ---
>  block.c           |    3 ++-
>  block/bochs.c     |    3 ++-
>  block/cow.c       |   12 ++++++++++--
>  block/qcow.c      |   22 ++++++++++++++++------
>  block/qcow2.c     |   37 +++++++++++++++++++++++++++++--------
>  block/raw-posix.c |    9 ++++++---
>  block/vmdk.c      |   38 ++++++++++++++++++++++++++++----------
>  block/vvfat.c     |   24 +++++++++++++++++-------
>  linux-user/mmap.c |    7 +++++--
>  linux-user/path.c |    6 +++++-
>  osdep.c           |    5 ++++-
>  slirp/misc.c      |    3 ++-
>  usb-linux.c       |    3 +--
>  vl.c              |   14 ++++++++++----
>  14 files changed, 137 insertions(+), 49 deletions(-)
>
> diff --git a/block.c b/block.c
> index aca5a6d..c78d66a 100644
> --- a/block.c
> +++ b/block.c
> @@ -371,7 +371,8 @@ int bdrv_open2(BlockDriverState *bs, const char *filename, int flags,
>              snprintf(backing_filename, sizeof(backing_filename),
>                       "%s", filename);
>          else
> -            realpath(filename, backing_filename);
> +            if (!realpath(filename, backing_filename))
> +                return -1;
>  
>          bdrv_qcow2 = bdrv_find_format("qcow2");
>          options = parse_option_parameters("", bdrv_qcow2->create_options, NULL);
> diff --git a/block/bochs.c b/block/bochs.c
> index bac81c4..0d614eb 100644
> --- a/block/bochs.c
> +++ b/block/bochs.c
> @@ -199,7 +199,8 @@ static inline int seek_to_sector(BlockDriverState *bs, int64_t sector_num)
>      // read in bitmap for current extent
>      lseek(s->fd, bitmap_offset + (extent_offset / 8), SEEK_SET);
>  
> -    read(s->fd, &bitmap_entry, 1);
> +    if (read(s->fd, &bitmap_entry, 1) != 1)
> +        return -1; // not allocated
>   

This is no more correct than before.  read() can return EINTR and that 
should be handled appropriately.  Elsewhere, read() can return partial 
results and we ought to handle that properly.

Using -D_FORTIFY_SOURCES=0 will eliminate these warnings.  If we're 
going to fix these things, we should fix them properly.

Regards,

Anthony Liguori