NAME

       io_uring_register_files - register file descriptors

SYNOPSIS

       #include <liburing.h>

       int io_uring_register_files(struct io_uring *ring,
                                   const int *files,
                                   unsigned nr_files);

       int io_uring_register_files_tags(struct io_uring *ring,
                                        const int *files,
                                        const __u64 *tags,
                                        unsigned nr);

       int io_uring_register_files_sparse(struct io_uring *ring,
                                          unsigned nr_files);

       int io_uring_register_files_update(struct io_uring *ring,
                                          unsigned off,
                                          const int *files,
                                          unsigned nr_files);

       int io_uring_register_files_update_tag(struct io_uring *ring,
                                          unsigned off,
                                          const int *files,
                                          const __u64 *tags,
                                          unsigned nr_files);

DESCRIPTION

       The  io_uring_register_files(3)  function  registers  nr_files  number of file descriptors defined by the
       array files belonging to the ring for subsequent operations.

       The io_uring_register_files_tags(3) function behaves the same as io_uring_register_files(3) function  but
       additionally takes tags parameter. See IORING_REGISTER_BUFFERS2 for the resource tagging description.

       The  io_uring_register_files_sparse(3)  function registers an empty file table of nr_files number of file
       descriptors. These files must be updated  before  use,  using  eg  io_uring_register_files_update_tag(3).
       Note   that   if   the   size   of   the   sparse   table   exceeds   what   RLIMIT_NOFILE  allows,  then
       io_uring_register_files_sparse(3) will attempt to raise the limit  using  setrlimit  (2)  and  retry  the
       operation.  If  the  registration  fails  after  doing  that, then an error will be returned.  The sparse
       variant is available in kernels 5.19 and later.

       Registering a file table is a prerequisite for using any request that uses direct descriptors.

       Registered files have less overhead per operation than normal files. This is due to the kernel grabbing a
       reference count on a file when an operation begins, and dropping it when it's done. When the process file
       table is shared, for example if the process has ever created any threads, then this  cost  goes  up  even
       more.  Using  registered  files  reduces  the  overhead of file reference management across requests that
       operate on a file.

       The io_uring_register_files_update(3) function updates existing registered files. The off  is  offset  on
       which to start the update nr_files number of files defined by the array files belonging to the ring.

       The  io_uring_register_files_update_tag(3) function behaves the same as io_uring_register_files_update(3)
       function but additionally takes tags parameter. See IORING_REGISTER_BUFFERS2  for  the  resource  tagging
       description.

RETURN VALUE

       On         success         io_uring_register_files(3),         io_uring_register_files_tags(3)        and
       io_uring_register_files_sparse(3)      return       0.        io_uring_register_files_update(3)       and
       io_uring_register_files_update_tag(3) return number of files updated.  On failure they return -errno.

SEE ALSO

       io_uring_register(2), io_uring_get_sqe(3), io_uring_unregister_files(3)

liburing-2.1                                    November 15, 2021                     io_uring_register_files(3)