The io_uring_register
syscall supports various registration ops to allow a user to register different resources that io_uring
can use.
Specifically, with IORING_REGISTER_PBUF_RING
combined with the IOU_PBUF_RING_MMAP
flag, the kernel allocates pages for an io_buffer_list
and attaches it to the io_ring_ctx
under a given bgid
.
int io_register_pbuf_ring(struct io_ring_ctx *ctx, void __user *arg)
{
struct io_uring_buf_reg reg;
struct io_buffer_list *bl, *free_bl = NULL;
int ret;
if (copy_from_user(®, arg, sizeof(reg)))
return -EFAULT;
/*...*/
if (!(reg.flags & IOU_PBUF_RING_MMAP))
ret = io_pin_pbuf_ring(®, bl);
else
ret = io_alloc_pbuf_ring(®, bl); // <-- IOU_PBUF_RING_MMAP
if (!ret) {
bl->nr_entries = reg.ring_entries;
bl->mask = reg.ring_entries - 1;
io_buffer_add_list(ctx, bl, reg.bgid); // <-- add buffer_list to ctx with bgid
return 0;
}
kfree(free_bl);
return ret;
}
In the io_alloc_pbuf_ring()
function below, the kernel uses __get_free_pages()
to allocate pages for the buffer ring:
static int io_alloc_pbuf_ring(struct io_uring_buf_reg *reg,
struct io_buffer_list *bl)
{
gfp_t gfp = GFP_KERNEL_ACCOUNT | __GFP_ZERO | __GFP_NOWARN | __GFP_COMP;
size_t ring_size;
void *ptr;
ring_size = reg->ring_entries * sizeof(struct io_uring_buf_ring);
ptr = (void *) __get_free_pages(gfp, get_order(ring_size));
if (!ptr)
return -ENOMEM;
bl->buf_ring = ptr;
bl->is_mapped = 1;
bl->is_mmap = 1;
return 0;
}
For more information click here.
Overview WhatsMyName is a free, community-driven OSINT tool designed to identify where a username exists…
Managing disk usage is a crucial task for Linux users and administrators alike. Understanding which…
Efficient disk space management is vital in Linux, especially for system administrators who manage servers…
Knowing how to check directory sizes in Linux is essential for managing disk space and…
Managing user accounts is a core responsibility for any Linux administrator. Whether you’re securing a…
Linux offers powerful command-line tools for system administrators to view and manage user accounts. Knowing…