rmsr.r_offset now is set to rqsr.r_offset plus the number of bytes
zeroed before hitting the end-of-file. After this change rmsr.r_offset
no longer contains the EOF when the requested operation range is
completely beyond the end-of-file. Instead in such case rmsr.r_offset is
equal to rqsr.r_offset. Callers can obtain the number of bytes zeroed
by subtracting rqsr.r_offset from rmsr.r_offset.
Sponsored by: The FreeBSD Foundation
Reviewed by: kib
Differential Revision: https://reviews.freebsd.org/D31677
rmacklem@ spotted two things in the system call:
- Upon returning from a successful operation, vop_stddeallocate can
update rmsr.r_offset to a value greater than file size. This behavior,
although being harmless, can be confusing.
- The EINVAL return value for rqsr.r_offset + rqsr.r_len > OFF_MAX is
undocumented.
This commit has the following changes:
- vop_stddeallocate and shm_deallocate to bound the the affected area
further by the file size.
- The EINVAL case for rqsr.r_offset + rqsr.r_len > OFF_MAX is
documented.
- The fspacectl(2), vn_deallocate(9) and VOP_DEALLOCATE(9)'s return
len is explicitly documented the be the value 0, and the return offset
is restricted to be the smallest of off + len and current file size
suggested by kib@. This semantic allows callers to interact better
with potential file size growth after the call.
Sponsored by: The FreeBSD Foundation
Reviewed by: imp, kib
Differential Revision: https://reviews.freebsd.org/D31604
fspacectl(2) is a system call to provide space management support to
userspace applications. VOP_DEALLOCATE(9) is a VOP call to perform the
deallocation. vn_deallocate(9) is a public KPI for kmods' use.
The purpose of proposing a new system call, a KPI and a VOP call is to
allow bhyve or other hypervisor monitors to emulate the behavior of SCSI
UNMAP/NVMe DEALLOCATE on a plain file.
fspacectl(2) comprises of cmd and flags parameters to specify the
space management operation to be performed. Currently cmd has to be
SPACECTL_DEALLOC, and flags has to be 0.
fo_fspacectl is added to fileops.
VOP_DEALLOCATE(9) is added as a new VOP call. A trivial implementation
of VOP_DEALLOCATE(9) is provided.
Sponsored by: The FreeBSD Foundation
Reviewed by: kib
Differential Revision: https://reviews.freebsd.org/D28347
