Messages in this thread | | | From | "Rafael J. Wysocki" <> | Subject | Re: [PATCH -mm 1/3] swsusp: Add ioctl for swap files support | Date | Fri, 29 Sep 2006 00:58:32 +0200 |
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On Friday, 29 September 2006 00:42, Andrew Morton wrote: > On Fri, 29 Sep 2006 00:13:38 +0200 > "Rafael J. Wysocki" <rjw@sisk.pl> wrote: > > > To be able to use swap files as suspend storage from the userland suspend > > tools we need an additional ioctl() that will allow us to provide the kernel > > with both the swap header's offset and the identification of the resume > > partition. > > > > The new ioctl() should be regarded as a replacement for the > > SNAPSHOT_SET_SWAP_FILE ioctl() that from now on will be considered as > > obsolete, but has to stay for backwards compatibility of the interface. > > > > + > > +/* > > + * This structure is used to pass the values needed for the identification > > + * of the resume swap area from a user space to the kernel via the > > + * SNAPSHOT_SET_SWAP_AREA ioctl > > + */ > > +struct resume_swap_area { > > + u_int16_t dev; > > + loff_t offset; > > +} __attribute__((packed)); > > > > hmm. Asking the compiler to pack 16-bit and 64-bit quantities in this > manner is a bit risky. I guess it'll do the right thing, consistently, > across all compiler versions and vendors and 32-bit-on-64-bit-kernel, etc. > > But from a defensiveness/paranoia POV it'd be better to use a u32 here, I > suspect. (Will access to that loff_t cause an alignment trap on ia64? Any > other CPUs? Dunno).
I'm not sure too. Will change it to a 32-bit value.
> > > #define PMOPS_PREPARE 1 > > #define PMOPS_ENTER 2 > > Index: linux-2.6.18-mm1/kernel/power/user.c > > =================================================================== > > --- linux-2.6.18-mm1.orig/kernel/power/user.c > > +++ linux-2.6.18-mm1/kernel/power/user.c > > @@ -343,6 +343,37 @@ OutS3: > > } > > break; > > > > + case SNAPSHOT_SET_SWAP_AREA: > > + if (data->bitmap) { > > + error = -EPERM; > > + } else { > > + struct resume_swap_area swap_area; > > + dev_t swdev; > > + > > + error = copy_from_user(&swap_area, (void __user *)arg, > > + sizeof(struct resume_swap_area)); > > + if (error) { > > + error = -EFAULT; > > + break; > > + } > > + > > + /* > > + * User space encodes device types as two-byte values, > > + * so we need to recode them > > + */ > > Really? stat() uses unsigned long and stat64() uses unsigned long long dev_t.
I don't know what the remaining 6 bytes are used for. Anyway we need to use old_decode_dev() to get this right.
> > + swdev = old_decode_dev(swap_area.dev); > > + if (swdev) { > > + offset = swap_area.offset; > > + data->swap = swap_type_of(swdev, offset); > > + if (data->swap < 0) > > + error = -ENODEV; > > + } else { > > + data->swap = -1; > > + error = -EINVAL; > > + } > > + } > > + break; > > + > > default: > > error = -ENOTTY; > > But I wonder if we need to pass the device identified into this ioctl at > all. What device is the ioctl() against? ie: what do `filp' and `inode' > point at? If it's /dev/hda1 then everything we need is right there, is it > not? > > ohshit, it's a miscdevice. I wonder if it would have defined all this > stuff to be operations against the blockdev. Perhaps not.
Nope. We need char-like read() and write().
> Well anyway. It might be neater to require that userspace open /dev/hda1 > and pass in the fd to this ioctl. But this code will never be neat, so > whatever.
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