On 03/01/2018 04:31 PM, Andrew Morton wrote: > On Thu, 1 Mar 2018 12:43:37 -0500 Waiman Long <longman@xxxxxxxxxx> wrote: > >> When minimum/maximum values are specified for a sysctl parameter in >> the ctl_table structure with proc_dointvec_minmax() handler, update >> to that parameter will fail with error if the given value is outside >> of the required range. >> >> There are use cases where it may be better to clamp the value of >> the sysctl parameter to the given range without failing the update, >> especially if the users are not aware of the actual range limits. >> Reading the value back after the update will now be a good practice >> to see if the provided value exceeds the range limits. >> >> To provide this less restrictive form of range checking, a new flags >> field is added to the ctl_table structure. The new field is a 16-bit >> value that just fits into the hole left by the 16-bit umode_t field >> without increasing the size of the structure. >> >> When the CTL_FLAGS_CLAMP_RANGE flag is set in the ctl_table entry, >> any update from the userspace will be clamped to the given range >> without error. >> >> ... >> >> --- a/include/linux/sysctl.h >> +++ b/include/linux/sysctl.h >> @@ -116,6 +116,7 @@ struct ctl_table >> void *data; >> int maxlen; >> umode_t mode; >> + uint16_t flags; > It would be nice to make this have type `enum ctl_table_flags', but I > guess there's then no reliable way of forcing it to be 16-bit. > I guess this is the best we can do... > > --- a/include/linux/sysctl.h~sysctl-add-flags-to-support-min-max-range-clamping-fix > +++ a/include/linux/sysctl.h > @@ -116,7 +116,7 @@ struct ctl_table > void *data; > int maxlen; > umode_t mode; > - uint16_t flags; > + uint16_t flags; /* enum ctl_table_flags */ > struct ctl_table *child; /* Deprecated */ > proc_handler *proc_handler; /* Callback for text formatting */ > struct ctl_table_poll *poll; > @@ -125,7 +125,7 @@ struct ctl_table > } __randomize_layout; > > /** > - * enum ctl_table_flags - flags for the ctl table > + * enum ctl_table_flags - flags for the ctl table (struct ctl_table.flags) > * > * @CTL_FLAGS_CLAMP_RANGE: Set to indicate that the entry should be > * flexibly clamped to min/max range in case the user provided The flags field is actually a bit mask of various bits defined in the enum type. So I will not change the type of flags to enum ctl_table_flags as it is not strictly an enum type. However, I can certainly add the suggested comment change in the next version of the patch. Cheers, Longman
