[libvirt] [PATCH v4 1/3] virFile: Add APIs for extended attributes handling

[Daniel P. Berrange]

On Fri, Mar 15, 2013 at 03:12:01PM +0100, Michal Privoznik wrote:
> Currently, only three wrappers are being implemented:
> virFileSetAttr for setting attributes
> virFileGetAttr for querying attributes (note we need to call it twice,
> first time to get length of attribute value, second to get actual value)
> virFileRemoveAttr for removing attributes
> ---
> 
> diff to v3:
> -set errno=ENOSYS when building without WITH_ATTR for easier check within callee.
> 
> diff to v2:
> -drop multiple check for libattr
> 
>  src/libvirt_private.syms |   3 ++
>  src/util/virfile.c       | 108 +++++++++++++++++++++++++++++++++++++++++++++++
>  src/util/virfile.h       |  14 ++++++
>  3 files changed, 125 insertions(+)
> 
> diff --git a/src/libvirt_private.syms b/src/libvirt_private.syms
> index 5cad990..5a2cbe8 100644
> --- a/src/libvirt_private.syms
> +++ b/src/libvirt_private.syms
> @@ -1252,8 +1252,11 @@ virFileClose;
>  virFileDirectFdFlag;
>  virFileFclose;
>  virFileFdopen;
> +virFileGetAttr;
>  virFileLoopDeviceAssociate;
> +virFileRemoveAttr;
>  virFileRewrite;
> +virFileSetAttr;
>  virFileTouch;
>  virFileUpdatePerm;
>  virFileWrapperFdClose;
> diff --git a/src/util/virfile.c b/src/util/virfile.c
> index 4a9fa81..be50e83 100644
> --- a/src/util/virfile.c
> +++ b/src/util/virfile.c
> @@ -37,6 +37,10 @@
>  # include <sys/ioctl.h>
>  #endif
>  
> +#ifdef WITH_ATTR
> +# include <attr/xattr.h>
> +#endif
> +
>  #include "vircommand.h"
>  #include "configmake.h"
>  #include "viralloc.h"
> @@ -644,3 +648,107 @@ int virFileLoopDeviceAssociate(const char *file,
>  }
>  
>  #endif /* __linux__ */
> +
> +#ifdef WITH_ATTR
> +int
> +virFileSetAttr(const char *file,
> +               const char *name,
> +               const char *value)
> +{
> +    size_t valueSize = strlen(value);
> +    if (setxattr(file, name, value, valueSize, 0) < 0) {
> +        virReportSystemError(errno,
> +                             _("Unable to set extended attribute '%s' on '%s'"),
> +                             name, file);
> +        return -1;
> +    }
> +    return 0;
> +}
> +
> +int
> +virFileGetAttr(const char *file,
> +               const char *name,
> +               char **value)
> +{
> +    int ret = -1;
> +    char *buf = NULL;
> +    ssize_t valueSize;
> +
> +    /* get attribute length */
> +    if ((valueSize = getxattr(file, name, NULL, 0)) < 0) {
> +        /* The Linux kernel does not define ENOATTR, but maps it to ENODATA. */
> +        if (errno == ENOATTR || errno == ENODATA) {
> +            *value = NULL;
> +            return 0;
> +        } else {
> +            virReportSystemError(errno,
> +                                 _("Unable to get extended attribute '%s' on '%s'"),
> +                                 name, file);
> +            return ret;
> +        }
> +    }
> +
> +    if (VIR_ALLOC_N(buf, valueSize) < 0) {
> +        virReportOOMError();
> +        return ret;
> +    }
> +
> +    if ((ret = getxattr(file, name, buf, valueSize)) < 0) {
> +        VIR_FREE(buf);
> +        virReportSystemError(errno,
> +                             _("Unable to get extended attribute '%s' on '%s'"),
> +                             name, file);
> +    } else {
> +        *value = buf;
> +    }
> +
> +    return ret;
> +}
> +
> +int
> +virFileRemoveAttr(const char *file,
> +                  const char *name)
> +{
> +    if (removexattr(file, name) < 0) {
> +        virReportSystemError(errno,
> +                             _("Unable to remove extended attribute '%s' on '%s'"),
> +                             name, file);
> +        return -1;
> +    }
> +    return 0;
> +}
> +
> +#else /* WITH_ATTR */
> +
> +int
> +virFileSetAttr(const char *file ATTRIBUTE_UNUSED,
> +               const char *name ATTRIBUTE_UNUSED,
> +               const char *value ATTRIBUTE_UNUSED)
> +{
> +    errno = ENOSYS;
> +    virReportSystemError(errno, "%s",
> +                         _("Unable to set extended attributes"));
> +    return -1;
> +}
> +
> +int
> +virFileGetAttr(const char *file ATTRIBUTE_UNUSED,
> +               const char *name ATTRIBUTE_UNUSED,
> +               char **value ATTRIBUTE_UNUSED)
> +{
> +    errno = ENOSYS;
> +    virReportSystemError(errno, "%s",
> +                         _("Unable to get extended attributes"));
> +    return -1;
> +}
> +
> +int
> +virFileRemoveAttr(const char *file ATTRIBUTE_UNUSED,
> +                  const char *name ATTRIBUTE_UNUSED)
> +{
> +    errno = ENOSYS;

NACK to this addition. Callers have absolutely no business accessing
'errno' for any function which uses libvirt error reporting - we make
no guarnatees that the value will be preserved by any cleanup code in
such methods. If callers want to check errno values they should do this:

  virErrorPtr err = virGetLastError()
  if (err &&
      err->code == VIR_ERR_SYSTEM_ERROR &&
      err->int1 == ENOSYS)
     ....

Regards,
Daniel
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