On Mon, Jun 8, 2020 at 9:51 AM Jesper Dangaard Brouer <brouer@xxxxxxxxxx> wrote: > > This patch change BPF syscall to avoid returning file descriptor value zero. > > As mentioned in cover letter, it is very impractical when extending kABI > that the file-descriptor value 'zero' is valid, as this requires new fields > must be initialised as minus-1. First step is to change the kernel such that > BPF-syscall simply doesn't return value zero as a FD number. > > This patch achieves this by similar code to anon_inode_getfd(), with the > exception of getting unused FD starting from 1. The kernel already supports > starting from a specific FD value, as this is used by f_dupfd(). It seems > simpler to replicate part of anon_inode_getfd() code and use this start from > offset feature, instead of using f_dupfd() handling afterwards. Wouldn't it be better to just handle that on libbpf side? That way it works on all kernels and doesn't require this duplication of logic inside kernel? > > Signed-off-by: Jesper Dangaard Brouer <brouer@xxxxxxxxxx> > --- > fs/file.c | 2 +- > include/linux/file.h | 1 + > kernel/bpf/syscall.c | 38 ++++++++++++++++++++++++++++++++------ > 3 files changed, 34 insertions(+), 7 deletions(-) > [...]
