Re: [PATCH v2 04/17] IB/core: Add umem function to read data from user-space

Yann Droneaud
2014-12-10T16:22:01Z

Hi,

Le mardi 11 novembre 2014 à 18:36 +0200, Haggai Eran a écrit :
> In some drivers there's a need to read data from a user space area that
> was pinned using ib_umem, when running from a different process context.
>
> The ib_umem_copy_from function allows reading data from the physical pages
> pinned in the ib_umem struct.
>
> Signed-off-by: Haggai Eran <haggaie-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>
> ---
> drivers/infiniband/core/umem.c | 26 ++++++++++++++++++++++++++
> include/rdma/ib_umem.h | 2 ++
> 2 files changed, 28 insertions(+)
>
> diff --git a/drivers/infiniband/core/umem.c b/drivers/infiniband/core/umem.c
> index e0f883292374..77bec75963e7 100644
> --- a/drivers/infiniband/core/umem.c
> +++ b/drivers/infiniband/core/umem.c
> @@ -292,3 +292,29 @@ int ib_umem_page_count(struct ib_umem *umem)
> return n;
> }
> EXPORT_SYMBOL(ib_umem_page_count);
> +
> +/*
> + * Copy from the given ib_umem's pages to the given buffer.
> + *
> + * umem - the umem to copy from
> + * offset - offset to start copying from
> + * dst - destination buffer
> + * length - buffer length
> + *
> + * Returns the number of copied bytes, or an error code.
> + */
> +int ib_umem_copy_from(struct ib_umem *umem, size_t offset, void *dst,
> + size_t length)

I would prefer the arguments in the same order as ib_copy_from_udata()

int ib_umem_copy_from(void *dst,
struct ib_umem *umem, size_t umem_offset,
size_t length);

> +{
> + size_t end = offset + length;
> +
> + if (offset > umem->length || end > umem->length || end < offset) {
> + pr_err("ib_umem_copy_from not in range. offset: %zd umem length: %zd end: %zd\n",
> + offset, umem->length, end);
> + return -EINVAL;
> + }
> +
> + return sg_pcopy_to_buffer(umem->sg_head.sgl, umem->nmap, dst, length,
> + offset + ib_umem_offset(umem));
> +}
> +EXPORT_SYMBOL(ib_umem_copy_from);

As the function return a "int", no more than INT_MAX bytes (likely 2^31
- 1) can be copied. Perhaps changing the return type to to ssize_t would
be better (and a check to enfore ssize_t maximum value). Or change the
function could return 0 in case of success or a error code, just like
ib_copy_from_udata().

> diff --git a/include/rdma/ib_umem.h b/include/rdma/ib_umem.h
> index 7ed6d4ff58dc..ee897724cbf8 100644
> --- a/include/rdma/ib_umem.h
> +++ b/include/rdma/ib_umem.h
> @@ -84,6 +84,8 @@ struct ib_umem *ib_umem_get(struct ib_ucontext *context, unsigned long addr,
> size_t size, int access, int dmasync);
> void ib_umem_release(struct ib_umem *umem);
> int ib_umem_page_count(struct ib_umem *umem);
> +int ib_umem_copy_from(struct ib_umem *umem, size_t start, void *dst,
> + size_t length);
>
> #else /* CONFIG_INFINIBAND_USER_MEM */
>