Messages in this thread | | | Date | Thu, 29 Oct 2015 15:39:32 +0100 | From | David Sterba <> | Subject | Re: [PATCH] btrfs: bugfix: handle FS_IOC32_{GETFLAGS,SETFLAGS,GETVERSION} in btrfs_ioctl |
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On Thu, Oct 29, 2015 at 08:22:34AM +0000, Luke Dashjr wrote: > > > I don't see what is different with that implementation. All > > > f2fs_compat_ioctl does is change cmd to the plain-IOC equivalent and > > > call f2fs_ioctl with the same arg (compat_ptr merely causes a cast to > > > void* and back, which AFAIK is a noop on 64-bit?). Am I missing > > > something? > > > > No, that's the idea. Add new calback for compat_ioctl, put it under > > #ifdef CONFIG_COMPAT and do the same number switch. > > Ok, someone else explained this to me. Please let me know if PATCHv2 (sent > separately) does not address the needed changes.
Patch is ok, thanks.
> > > I could try to just imitate it, but > > > I'd rather know what is significant/going on to ensure I don't waste your > > > time with code I don't even properly understand myself. > > > > > > Perhaps by coincidence, the patch does at least in practice work > > > (although at least `btrfs send` appears to be broken still, and I'm at a > > > loss for how to approach fixing that). > > > > The 'receive' 32bit/64bit was broken due to size difference in the ioctl > > structure that led to different ioctl. This is transparently fixed, see > > BTRFS_IOC_SET_RECEIVED_SUBVOL_32 at the top of ioctl.c. > > > > In what way is SEND broken? There are only u64/s64 members in > > btrfs_ioctl_send_args, I don't see how this could break on 32/64 > > userspace/kernel. > > I've investigated this now, and it seems to be the pointer-type clone_sources > member of struct btrfs_ioctl_send_args. I can't think of a perfect way to fix > this, but it might not be *too* ugly to: > - replace the current clone_sources with a u64 that must always be (u64)-1; > this causes older kernels to error cleanly if called with a new ioctl data > - use the top 1 or 2 bits of flags to indicate sizeof(void*) as it appears to > userspace OR just use up reserved[0] for pointer size: > io_send.ptr_size = sizeof(void*); > - replace one of the reserved fields with the new clone_sources
All the change seem too intrusive or not so easy to use.
I suggest to add an anonymous union and add a u64 member that would force the type width:
struct btrfs_ioctl_send_args { __s64 send_fd; /* in */ __u64 clone_sources_count; /* in */ union { __u64 __user *clone_sources; /* in */ u64 __pointer_alignment; }; __u64 parent_root; /* in */ __u64 flags; /* in */ __u64 reserved[4]; /* in */ };
> The way it was done for receive seems like it might not work for non-x86 > compat interfaces (eg, MIPS n32) - but I could be wrong.
Possible, but I don't see right now how it would not work on eg. mips32. unless sizeof(long) is 8 bytes there and CONFIG_64BIT is not defined.
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