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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?sX0P8B99IWD7lez/aiSsiFDM4C716NOI0Xm6o3PUYuGLDKKLtS77pAjBsZfq?= =?us-ascii?Q?a+uDcSjgtfXmnvRYn9Aqty2MLtN0wdG1GbsNI1mWMHZ8KYavkxaaHdxDagIR?= =?us-ascii?Q?vdirUiFondoAyyOtRjar5YjYq7BxDe5o3pAlz7PuIgLZNJwmcDa7LeEfWTl1?= =?us-ascii?Q?vN6IP6BKK04Qyk/EMQtHXVJ4IRy7+LDUkfjBuue6xDgoKGCi6WD7V/AH+5zT?= =?us-ascii?Q?LtgUQ8kkmnLyQhegnU5sCBUh546r6J1CnKALKWsvsUI0uOjuoOECWsdcq+BC?= =?us-ascii?Q?P/H3Ua2b6aFbVSMfrACqKiLkEfULzT7R00ud6H6/NftSArFE9oIdkOQO3th7?= =?us-ascii?Q?6lNam+nFroWcWYIgV15ldScA2ADhWjBnsjkOSxONiB46Kl5m6lP2TrSSgc5s?= =?us-ascii?Q?ryr7MxHPRoQDwV2vpSoIB1UtC0NxEiDgPdNQtWyIWvVY/dCsm3MkwDI7ICcm?= =?us-ascii?Q?P2VKHZvqpWRa9mjfD+xWvgi5O2ba+Z1js3WqZTSDFZwWWb8z7zHSCIY84zql?= =?us-ascii?Q?EzYhUyhGt+tluWfJZ+9OP7sjgXpv+wNw/noC9/BJaHyousm5PifzCF0kDJs3?= =?us-ascii?Q?MVUXAOsbzPIvkkrmOcRDOPmxf1hlBVSoy/HCBSXhI1DL6Zuno28vvosxJFqh?= =?us-ascii?Q?zSyNtOmNymFZ4DjhfhGDEsmc8jdLnylIxg+fJdBzNwtOWo8W11o09x/r8tlU?= =?us-ascii?Q?NJz88qMsvBex6GXkjuP4gKTsUqnhu8EWWzMIPmP+Be1fcs6kXTGprz7GGYn7?= =?us-ascii?Q?oqe1jVoysQ/D0zh7J/X8s+V84nBU+WwQ60m7OGJkeMFrre3jrkttGY5dJxB/?= =?us-ascii?Q?VyBMhS/aXCx/NW7+yz/rr/iCcxb/hjMdS5u53ugKJzlUWVpeuQqa1/bVomhC?= =?us-ascii?Q?MHo8hf7Qt7oyRfpJvOzpqRljdPr54WWuq2DsAyVKx02+s3yH+dmyDsu038Gm?= =?us-ascii?Q?ukIRhV2++ZvyO2PcXUMr4kGUd0QQpYpBusqUNyLcANkGnUupU6lOkivf/PjN?= =?us-ascii?Q?OZiypagD67wHVeaZeRw7SB12z815UsYbNcqrWoVaIPWNCnRyrEu2QsD/gdSp?= =?us-ascii?Q?lm84c7TO5IgkdLPXAXGJYZ80BW159X4nHpasCcGJ9S3Ga/K5+nHHR6Rl8oV1?= =?us-ascii?Q?xoDB8oZ0oJmP+Hu3fWojdIHcujtnSXPm7jZusx1VIdzbntolNKBNU0VWdYfp?= =?us-ascii?Q?lC0UUvLgjH5mBzV9icTDIwQMpa7b+U3vnLH/wykybApJOfglq9meGTtX3Jna?= =?us-ascii?Q?LDgiFvO1XoVvdVoD72jo/gIiyJMIDXNThdCM6SOxA2UXsUzMHh4uKiKoA/rw?= =?us-ascii?Q?Xu5AxQUh8dtvNzB1XwUnmqI+EvL/90HLOdm/Dlc7y4+TtGUEPwcZWwKE/UY/?= =?us-ascii?Q?gR5CL0jsuhHjJ27ypyXYSA5jkJAf+LaOiTLQFyptlUZcV2fzEf+z6NfSkRDu?= =?us-ascii?Q?fggg1yJ+6fm+GB8j8Btgh71yAP20QgBoyYLXrU6MWZs9bVS6q089u3aMSubG?= =?us-ascii?Q?39swy4g8aeGJuB+v4VkRuPE9lTD0xySu8PX8e1EpMom2YJa+GYQ0kGgxzAXK?= =?us-ascii?Q?LeQ7fjW6N/9VA1mpUyzWBOYgvNT7qLiie4KpS/Uasvqc/2t8SYU3/wT5j+5g?= =?us-ascii?Q?nA=3D=3D?= X-MS-Exchange-CrossTenant-Network-Message-Id: 1c67fdf2-3822-402b-9b86-08dc670f174d X-MS-Exchange-CrossTenant-AuthSource: PH8PR11MB8107.namprd11.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 27 Apr 2024 23:09:29.3906 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 46c98d88-e344-4ed4-8496-4ed7712e255d X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: SV1kSUpQSzwqaXmV7OQVthLfXKmVjzCUR5EheLk9RF+0zYcawzVnd7IvmcbulrqBPulsISeGpVoA9f2GdlXGalSSMjUB/D+XZPtbz9xcV/M= X-MS-Exchange-Transport-CrossTenantHeadersStamped: SA1PR11MB7131 X-OriginatorOrg: intel.com Dan Williams wrote: > Dan Williams wrote: > > Lukas Wunner wrote: > > > On Sat, Apr 27, 2024 at 09:49:41AM -0700, Dan Williams wrote: > > > > Lukas Wunner wrote: > > > > > But I want to raise awareness that the inability to hide > > > > > empty attribute groups feels awkward. > > > > > > > > That is fair, it was definitely some gymnastics to only change user > > > > visible behavior for new "invisible aware" attribute groups that opt-in > > > > while leaving all the legacy cases alone. > > > > > > > > The concern is knowing when it is ok to call an is_visible() callback > > > > with a NULL @attr argument, or knowing when an empty array actually > > > > means "hide the group directory". > > > > > > > > We could add a sentinel value to indicate "I am an empty attribute list > > > > *AND* I want my directory hidden by default". However, that's almost > > > > identical to requiring a placeholder attribute in the list just to make > > > > __first_visible() happy. > > > > > > > > Other ideas? > > > > > > Perhaps an optional ->is_group_visible() callback in struct attribute_group > > > which gets passed only the struct kobject pointer? > > > > > > At least for PCI device authentication, that would be sufficient. > > > I could get from the kobject to the corresponding struct device, > > > then determine whether the device supports authentication or not. > > > > > > Because it's a new, optional callback, there should be no compatibility > > > issues. The SYSFS_GROUP_INVISIBLE return code from the ->is_visible() > > > call for individual attributes would not be needed then, at least in my > > > use case. > > > > That's where I started with this, but decided it was overkill to > > increase the size of that data structure globally for a small number of > > use cases. > > Perhaps could try something like this: > > diff --git a/fs/sysfs/group.c b/fs/sysfs/group.c > index d22ad67a0f32..f4054cf08e58 100644 > --- a/fs/sysfs/group.c > +++ b/fs/sysfs/group.c > @@ -33,11 +33,23 @@ static void remove_files(struct kernfs_node *parent, > > static umode_t __first_visible(const struct attribute_group *grp, struct kobject *kobj) > { > - if (grp->attrs && grp->attrs[0] && grp->is_visible) > - return grp->is_visible(kobj, grp->attrs[0], 0); > + if (grp->attrs && grp->is_visible) { > + struct attribute *attr = grp->attrs[0]; > + struct attribute empty_attr = { 0 }; > > - if (grp->bin_attrs && grp->bin_attrs[0] && grp->is_bin_visible) > - return grp->is_bin_visible(kobj, grp->bin_attrs[0], 0); > + if (!attr) > + attr = &empty_attr; > + return grp->is_visible(kobj, attr, 0); > + } > + > + if (grp->bin_attrs && grp->is_bin_visible) { > + struct bin_attribute *bin_attr = grp->bin_attrs[0]; > + struct bin_attribute empty_bin_attr = { 0 }; > + > + if (!bin_attr) > + bin_attr = &empty_bin_attr; > + return grp->is_bin_visible(kobj, bin_attr, 0); > + } > > return 0; > } > > ...because it is highly likely that existing is_visible() callers will > return @attr->mode when they do not recognize the attribute. But this > could lead to some subtle bugs if something only checks the attribute > index value. For example: > > lbr_is_visible(struct kobject *kobj, struct attribute *attr, int i) > { > /* branches */ > if (i == 0) > return x86_pmu.lbr_nr ? attr->mode : 0; > > return (x86_pmu.flags & PMU_FL_BR_CNTR) ? attr->mode : 0; > } > > ...but in this case we get lucky because it would return attr->mode > which is 0. Oh, but if an is_visible() callback gets confused by empty_attr, that's detectable: mode = grp->is_visible(kobj, attr, 0); if ((mode & ~SYSFS_GROUP_INVISIBLE) && attr == empty_attr) return 0; ..i.e. the only acceptable responses to an empty_attr check is 0 or ~SYSFS_GROUP_INVISIBLE.