February 27, 2026 at 18:21, "Sebastian Andrzej Siewior" <[email protected] mailto:[email protected]?to=%22Sebastian%20Andrzej%20Siewior%22%20%3Cbigeasy%40linutronix.de%3E > wrote:
> > On 2026-02-27 10:17:29 [+0000], Jiayuan Chen wrote: > > > > > bond_mode can be changed after device creation via sysfs or netlink, a bond > > created > > in active-backup mode can later be switched to round-robin, which means > > the allocation > > must not be conditional on the mode at creation time. > > > Must the device be in down state or can this be also changed while the > device is up? > > Sebastian > The mode change requires the device to be DOWN. BOND_OPT_MODE is defined with BOND_OPTFLAG_IFDOWN, and bond_opt_check_flags() enforces this: if ((opt->flags & BOND_OPTFLAG_IFDOWN) && (bond->dev->flags & IFF_UP)) return -EBUSY; The same restriction applies to the netlink path as well. Both sysfs and netlink go through __bond_opt_set() → bond_opt_check_deps(), which enforces BOND_OPTFLAG_IFDOWN for mode change. Attempting to change the mode while the device is UP returns -EBUSY regardless of how the change is requested. So unconditional allocation in bond_init() covers all cases: whether the device is created in round-robin mode, or switched to round-robin later (which requires being DOWN, meaning bond_open() hasn't been called with the new mode yet). Thanks,
