[libvirt] [PATCH v2 3/3] virstoragefile: Refactor virStorageFileResize

[Ján Tomko]

On 08/11/2014 10:30 PM, John Ferlan wrote:
> Currently virStorageFileResize() function uses build conditionals to
> choose either the posix_fallocate() or mmap() with no fallback in order
> to preallocate the space in the newly resized file.
> 
> This patch will modify the logic in order to allow fallbacks in the event
> that posix_fallocate() or the sys_fallocate syscall() doesn't work properly.
> The fallback will be to use the slow safewrite of zero filled buffers to
> the file.
> 
> Use the virFileFdPosixFallocate() rather than a local function.
> 
> Signed-off-by: John Ferlan <jferlan at redhat.com>
> ---
>  src/util/virstoragefile.c | 52 +++++++++++++++++++++++++++++++----------------
>  1 file changed, 34 insertions(+), 18 deletions(-)
> 
> diff --git a/src/util/virstoragefile.c b/src/util/virstoragefile.c
> index 5b6b2f5..4d37de1 100644
> --- a/src/util/virstoragefile.c
> +++ b/src/util/virstoragefile.c
> @@ -1086,6 +1086,39 @@ virStorageFileChainGetBroken(virStorageSourcePtr chain,
>      return 0;
>  }
>  
> +static int
> +resizeSysFallocate(const char *path,
> +                   int fd,
> +                   off_t offset,
> +                   off_t len)
> +{
> +    int rc = -1;
> +#if HAVE_SYS_SYSCALL_H && defined(SYS_fallocate)
> +    if ((rc = syscall(SYS_fallocate, fd, 0, offset, len)) != 0) {
> +        virReportSystemError(errno,
> +                             _("Failed to pre-allocate space for "
> +                             "file '%s'"), path);

I think this should not log an error, since we have a fallback.
VIR_DEBUG maybe?

> +    }
> +#endif
> +    return rc;
> +}
> +
> +static int
> +doResize(const char *path,
> +         int fd,
> +         off_t offset,
> +         off_t len)
> +{
> +    if (virFileFdPosixFallocate(fd, offset, len) == 0 ||
> +        resizeSysFallocate(path, fd, offset, len) == 0 ||
> +        safezero(fd, offset, len) == 0)
> +        return 0;
> +
> +    virReportError(VIR_ERR_OPERATION_UNSUPPORTED, "%s",
> +                   _("preallocate is not supported on this platform"));
> +    return -1;

safezero is always supported. And this function should do:
return safezero(fd, offset, len);


> +}
> +
>  
>  /**
>   * virStorageFileResize:
> @@ -1113,25 +1146,8 @@ virStorageFileResize(const char *path,
>      }
>  
>      if (pre_allocate) {
> -#if HAVE_POSIX_FALLOCATE
> -        if ((rc = posix_fallocate(fd, offset, len)) != 0) {
> -            virReportSystemError(rc,
> -                                 _("Failed to pre-allocate space for "
> -                                   "file '%s'"), path);
> -            goto cleanup;
> -        }
> -#elif HAVE_SYS_SYSCALL_H && defined(SYS_fallocate)
> -        if (syscall(SYS_fallocate, fd, 0, offset, len) != 0) {
> -            virReportSystemError(errno,
> -                                 _("Failed to pre-allocate space for "
> -                                   "file '%s'"), path);
> +        if (doResize(path, fd, offset, len) < 0)
>              goto cleanup;
> -        }
> -#else
> -        virReportError(VIR_ERR_OPERATION_UNSUPPORTED, "%s",
> -                       _("preallocate is not supported on this platform"));
> -        goto cleanup;
> -#endif
>      } else {
>          if (ftruncate(fd, capacity) < 0) {
>              virReportSystemError(errno,
> 


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