[libvirt] [PATCH] util: Implement and use virFileIsRegular() rather than d_type

[Eric Blake]

On 06/06/2018 11:37 AM, Stefan Berger wrote:
> The dirent's d_type field is not portable to all platforms. So we have
> to use stat() to determine the type of file for the functions that need
> to be cross-platform. Fix virFileChownFiles() by calling the new
> virFileIsRegular() function.
> 
> Signed-off-by: Stefan Berger <stefanb at linux.vnet.ibm.com>
> ---
>   src/libvirt_private.syms |  1 +
>   src/util/virfile.c       | 17 +++++++++++++----
>   src/util/virfile.h       |  1 +
>   3 files changed, 15 insertions(+), 4 deletions(-)

> +
> +bool
> +virFileIsRegular(const char *path)
> +{
> +    struct stat s;
> +    return (stat(path, &s) == 0) && S_ISREG(s.st_mode);

This always does a stat.

> +}
> +
> +
>   /**
>    * virFileExists: Check for presence of file
>    * @path: Path of file to check
> @@ -3005,12 +3014,13 @@ int virFileChownFiles(const char *name,
>           return -1;
>   
>       while ((direrr = virDirRead(dir, &ent, name)) > 0) {
> -        if (ent->d_type != DT_REG)
> -            continue;

And this was the non-portable code you're getting rid of, which was 
already buggy - even on systems with d_type, a return of DT_UNKNOWN 
requires a stat() rather than a blind continue.  However, your 
replacement is pessimizing platforms where d_type is reliable, by making 
us do a stat() where we previously did not need to.

Better would be using macros that use d_type where possible, and fall 
back to stat() only when d_type does not exist or is DT_UNKNOWN; for 
example, here's how gnulib does it:

#if HAVE_STRUCT_DIRENT_D_TYPE
/* True if the type of the directory entry D is known.  */
# define DT_IS_KNOWN(d) ((d)->d_type != DT_UNKNOWN)
/* True if the type of the directory entry D must be T.  */
# define DT_MUST_BE(d, t) ((d)->d_type == (t))
# define D_TYPE(d) ((d)->d_type)
#else
# define DT_IS_KNOWN(d) false
# define DT_MUST_BE(d, t) false
# define D_TYPE(d) DT_UNKNOWN

# undef DT_UNKNOWN
# define DT_UNKNOWN 0

(although we have to be careful with licensing, because that is from 
lib/fts.c which is marked GPLv3+).

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org