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SubjectRe: [PATCH 18/41] regset: new method and helpers for it
On Tue, Jun 30, 2020 at 09:53:12AM -0700, Linus Torvalds wrote:
> On Tue, Jun 30, 2020 at 6:25 AM Al Viro <viro@zeniv.linux.org.uk> wrote:
> >
> > How about ->regset_get()?
>
> Sounds good to me. And if you ever do something similar for 'set', you
> have a natural name to pick.

Umm... Something similar for 'set' would, AFAICS, work reasonably well
with the following primitives.
membuf_read(&from, data, size) -- copy min(size, amount left)
membuf_fetch(&from, data) -- copy min(sizeof(data), amount left) into data
(obviously a macro)
membuf_skip(&from, size) -- obvious
membuf_pick(&from, size), along the lines of
if (unlikely(size > p->left)
return ERR_PTR(-EINVAL);
res = p->p;
p->p += size;
p->left -= size;
return res;

So it would be something like

int regset_tls_set(struct task_struct *target, const struct user_regset *regset,
struct membuf from)
{
const struct user_desc *info;
int n = from.left / sizeof(*info);
int i;

info = membuf_pick(&from, n * sizeof(*info)); // can't fail here
for (i = 0; i < n; i++)
if (!tls_desc_okay(info + i))
return -EINVAL;

set_tls_desc(target, GDT_ENTRY_TLS_MIN, info, n);
return 0;
}

and

static int genregs32_set(struct task_struct *target,
const struct user_regset *regset,
struct membuf from)
{
int err;
unsigned pos, v;

for (pos = 0; from.left; pos += sizeof(u32)) {
membuf_fetch(&from, v);
err = putreg32(target, pos, v);
if (err)
return err;
}
return 0;
}

or

/*
* Copy the supplied 64-bit NT_MIPS_DSP buffer to the DSP context.
*/
static int dsp64_set(struct task_struct *target,
const struct user_regset *regset,
struct membuf from)
{
if (!cpu_has_dsp)
return -EIO;

membuf_read(&from, target->thread.dsp.dspr, NUM_DSP_REGS * sizeof(u64));
return membuf_read(&from, target->thread.dsp.dspcontrol, sizeof(u64));
}

etc.

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