NAME

       io_uring_prep_openat2 - prepare an openat2 request

SYNOPSIS

       #include <sys/types.h>
       #include <sys/stat.h>
       #include <fcntl.h>
       #include <linux/openat2.h>
       #include <liburing.h>

       void io_uring_prep_openat2(struct io_uring_sqe *sqe,
                                  int dfd,
                                  const char *path,
                                  int flags,
                                  struct open_how *how);

       void io_uring_prep_openat2_direct(struct io_uring_sqe *sqe,
                                         int dfd,
                                         const char *path,
                                         int flags,
                                         struct open_how *how,
                                         unsigned file_index);

DESCRIPTION

       The  io_uring_prep_openat2(3)  function  prepares an openat2 request. The submission queue
       entry sqe is setup to use the directory file  descriptor  dfd  to  start  opening  a  file
       described  by  path and using the open flags in flags and using the instructions on how to
       open the file given in how.

       For a direct descriptor open request, the offset is specified by the file_index  argument.
       Direct  descriptors are io_uring private file descriptors. They avoid some of the overhead
       associated with thread shared file tables, and can be used in any  io_uring  request  that
       takes  a  file descriptor. To do so, IOSQE_FIXED_FILE must be set in the SQE flags member,
       and the SQE fd field should use the direct descriptor value rather than the  regular  file
       descriptor. Direct descriptors are managed like registered files.

       If  the  direct  variant  is used, the application must first have registered a file table
       using io_uring_register_files(3) of the appropriate size. Once registered, a direct accept
       request  may  use  any  entry  in  that  table,  as  long  as it is within the size of the
       registered table.  If a specified entry already contains a file, the file  will  first  be
       removed  from  the  table  and  closed.  It's  consistent with the behavior of updating an
       existing file with io_uring_register_files_update(3).  Note that old kernels  don't  check
       the  SQE  file_index  field, which is not a problem for liburing helpers, but users of the
       raw  io_uring  interface  need  to  zero  SQEs   to   avoid   unexpected   behavior.    If
       IORING_FILE_INDEX_ALLOC  is  used  as the file_index for a direct open, then io_uring will
       allocate a free direct descriptor in the  existing  table.  The  allocated  descriptor  is
       returned  in  the CQE res field just like it would be for a non-direct open request. If no
       more entries are available in the direct descriptor table, -ENFILE is returned instead.

       These functions prepare an async openat2(2) request. See that man page for details.

RETURN VALUE

       None

ERRORS

       The CQE res field will contain the result of the operation. See the related man  page  for
       details  on  possible  values.  Note that where synchronous system calls will return -1 on
       failure and set errno to the actual error value, io_uring never uses  errno.   Instead  it
       returns the negated errno directly in the CQE res field.

NOTES

       As with any request that passes in data in a struct, that data must remain valid until the
       request has been successfully submitted. It need not remain valid until completion. Once a
       request  has  been  submitted,  the in-kernel state is stable. Very early kernels (5.4 and
       earlier) required state to be stable until the completion occurred. Applications can  test
       for  this  behavior  by  inspecting  the  IORING_FEAT_SUBMIT_STABLE  flag passed back from
       io_uring_queue_init_params(3).

SEE ALSO

       io_uring_get_sqe(3), io_uring_submit(3), io_uring_register(2), openat2(2)