Messages in this thread | | | Date | Tue, 21 Dec 2021 07:39:24 +0100 | Subject | Re: [PATCH 2/2] nvmem: expose NVMEM cells in sysfs | From | Rafał Miłecki <> |
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On 21.12.2021 07:33, Greg Kroah-Hartman wrote: > On Mon, Dec 20, 2021 at 09:39:43PM +0100, Rafał Miłecki wrote: >> Hi Greg, >> >> On 20.12.2021 09:00, Greg Kroah-Hartman wrote: >>> On Mon, Dec 20, 2021 at 07:47:30AM +0100, Rafał Miłecki wrote: >>>> static void nvmem_cell_entry_add(struct nvmem_cell_entry *cell) >>>> { >>>> + struct device *dev = &cell->nvmem->dev; >>>> + int err; >>>> + >>>> mutex_lock(&nvmem_mutex); >>>> list_add_tail(&cell->node, &cell->nvmem->cells); >>>> mutex_unlock(&nvmem_mutex); >>>> + >>>> + sysfs_attr_init(&cell->battr.attr); >>>> + cell->battr.attr.name = cell->name; >>>> + cell->battr.attr.mode = 0400; >>>> + cell->battr.read = nvmem_cell_attr_read; >>>> + err = sysfs_add_bin_file_to_group(&dev->kobj, &cell->battr, >>>> + nvmem_cells_group.name); >>> >>> Why not just use the is_bin_visible attribute instead to determine if >>> the attribute should be shown or not instead of having to add it >>> after-the-fact which will race with userspace and loose? >> >> I'm sorry I really don't see how you suggest to get it done. >> >> I can use .is_bin_visible() callback indeed to respect nvmem->root_only. > > Great. > >> I don't understand addig-after-the-fact part. How is .is_bin_visible() >> related to adding attributes for newly created cells? > > You are adding a sysfs attribute to a device that is already registered > in the driver core, and so the creation of that attribute is never seen > by userspace. The attribute needs to be attached to the device _BEFORE_ > it is registered. > > Also, huge hint, if a driver has to call as sysfs_*() call, something is > wrong. > >> Do you mean I can >> avoid calling sysfs_add_bin_file_to_group()? > > Yes. > >> Do you recall any existing example of such solution? > > Loads. > > Just add this attribute group to your driver as a default attribute > group and the driver core will create it for you if needed. > > Or if you always need it, no need to mess sith is_bin_visible() at all, > I can't really understand what you are trying to do here at all.
Thanks a lot! In nvmem_register() first there is a call to the device_register() and only later cells get added. I suppose I just have to rework nvmem_register() order so that: 1. Cells are collected earlier. For each cell I allocate group attribute 2. device_register() gets called
Thank you for explaining that with patience.
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