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SubjectRe: [PATCH -mm 1/3] swsusp: Add ioctl for swap files support
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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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