> Date: Mon, 26 Jun 2023 18:13:17 -0400 > From: Theodore Preduta <t...@pta.gg> > > Is it possible to create a vnode for a regular file in a file system > without linking the vnode to any directory, so that it disappears when > all open file descriptors to it are closed? (As far as I can tell, this > isn't possible with any of the vn_* or VOP_* functions?) > > If this idea is indeed not possible, should/could I implement something > like this? (If so, how?) > > For context, I'm currently working on implementing memfd_create(2), and > thought this might be a shortcut. Otherwise, I'll have to implement it > in terms of uvm operations (which is fine, just more work).
For a syscall, you should implement it in terms of uvm anonymous objects: - memfd_create: fd_allocfile, uao_create - .fo_close: uao_detach - .fo_read/write: ubc_uiomove (tricky bit: if the offset pointer is &fp->f_offset, you must acquire and release fp->f_lock around it) - .fo_mmap: just take a reference and return the object Should be easy, and similar to what kern_ksyms.c already does. No need for vnodes to be involved at all.
