Re: [Libguestfs] [PATCH nbdkit 4/7] cache, cow: Use full pread/pwrite operations
On Mon, Jul 26, 2021 at 06:28:57PM +0100, Richard W.M. Jones wrote:
Although it probably cannot happen on Linux, POSIX allows
pread/pwrite
to return or write fewer bytes than requested. The cache and cow
filters didn't handle this situation. Replace the raw
pread(2)/pwrite(2) syscalls with alternate versions which can handle
this.
Short reads and writes are unlikely to happen for regular files, but
are a definite possibility on named FIFOs, as well as block and char
devices. While our local cache happens to use a regular file, it is
indeed always better practice to write robust code.
---
common/utils/Makefile.am | 1 +
common/utils/utils.h | 2 +
common/utils/full-rw.c | 81 ++++++++++++++++++++++++++++++++++++++++
filters/cache/blk.c | 10 ++---
filters/cow/blk.c | 6 +--
5 files changed, 92 insertions(+), 8 deletions(-)
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3266
Virtualization: qemu.org | libvirt.org