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 TZOPdmUr 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wrote: > > On Wed, Apr 30, 2025 at 11:58:14PM +0200, David Hildenbrand wrote: > > > On 30.04.25 21:54, Lorenzo Stoakes wrote: > > > > Provide a means by which drivers can specify which fields of those > > > > permitted to be changed should be altered to prior to mmap()'ing a > > > > range (which may either result from a merge or from mapping an entirely new > > > > VMA). > > > > > > > > Doing so is substantially safer than the existing .mmap() calback which > > > > provides unrestricted access to the part-constructed VMA and permits > > > > drivers and file systems to do 'creative' things which makes it hard to > > > > reason about the state of the VMA after the function returns. > > > > > > > > The existing .mmap() callback's freedom has caused a great deal of issues, > > > > especially in error handling, as unwinding the mmap() state has proven to > > > > be non-trivial and caused significant issues in the past, for instance > > > > those addressed in commit 5de195060b2e ("mm: resolve faulty mmap_region() > > > > error path behaviour"). > > > > > > > > It also necessitates a second attempt at merge once the .mmap() callback > > > > has completed, which has caused issues in the past, is awkward, adds > > > > overhead and is difficult to reason about. > > > > > > > > The .mmap_proto() callback eliminates this requirement, as we can update > > > > fields prior to even attempting the first merge. It is safer, as we heavily > > > > restrict what can actually be modified, and being invoked very early in the > > > > mmap() process, error handling can be performed safely with very little > > > > unwinding of state required. > > > > > > > > Update vma userland test stubs to account for changes. > > > > > > > > Signed-off-by: Lorenzo Stoakes > > > > > > > > > I really don't like the "proto" terminology. :) > > > > > > [yes, David and his naming :P ] > > > > > > No, the problem is that it is fairly unintuitive what is happening here. > > > > > > Coming from a different direction, the callback is trigger after > > > __mmap_prepare() ... could we call it "->mmap_prepare" or something like > > > that? (mmap_setup, whatever) > > > > > > Maybe mmap_setup and vma_setup_param? Just a thought ... > > > > Haha that's fine, I'm not sure I love 'proto' either to be honest, naming is > > hard... > > > > I would rather not refer to VMA's at all to be honest, if I had my way, no > > driver would ever have access to a VMA at all... > > > > But mmap_setup() or mmap_prepare() sound good! > > +1 > > and struct vm_area_desc maybe? That's nice actually thanks, will do! > > > > > > > > > > In general (although it's late in Germany), it does sound like an > > > interesting approach. > > > > Thanks! Appreciate it :) I really want to attack this, as I _hate_ how we > > effectively allow drivers to do _anything_ with VMAs like this. > > > > Yes, hate-driven development... > > Just move vm_area_struct to mm/internal.h and let them cope :-D Haha oh man the dream. Though it'd be vma.h of course :P > > -- > Sincerely yours, > Mike. Cheers, Lorenzo