Re: [libvirt RFCv4 04/20] runio: add arguments to extend use beyond just stdin and stdout

On Thu, Apr 28, 2022 at 06:24:11PM +0200, Claudio Fontana wrote: > On 4/28/22 2:54 PM, Daniel P. Berrangé wrote: >> On Wed, Apr 27, 2022 at 11:13:23PM +0200, Claudio Fontana wrote: >>> add arguments to runio to allow read/write from/to arbitrary >>> file descriptors, as opposed to just stdin and stdout. >>> >>> Signed-off-by: Claudio Fontana <cfontana(a)suse.de&gt; >>> --- >>> src/util/iohelper.c | 2 +- >>> src/util/runio.c | 10 +++++----- >>> src/util/runio.h | 17 ++++++++++++++++- >>> 3 files changed, 22 insertions(+), 7 deletions(-) >>> >>> diff --git a/src/util/iohelper.c b/src/util/iohelper.c >>> index 5a0098542e..93674c1e2f 100644 >>> --- a/src/util/iohelper.c >>> +++ b/src/util/iohelper.c >>> @@ -96,7 +96,7 @@ main(int argc, char **argv) >>> usage(EXIT_FAILURE); >>> } >>> >>> - if (fd < 0 || runIO(path, fd, oflags) < 0) >>> + if (fd < 0 || runIO(path, fd, oflags, STDIN_FILENO, STDOUT_FILENO) < 0) >>> goto error; >>> >>> return 0; >>> diff --git a/src/util/runio.c b/src/util/runio.c >>> index a7b902af7e..f42acddae9 100644 >>> --- a/src/util/runio.c >>> +++ b/src/util/runio.c >>> @@ -134,7 +134,7 @@ runIOCopy(const struct runIOParams p) >>> >>> >>> off_t >>> -runIO(const char *path, int fd, int oflags) >>> +runIO(const char *path, int fd, int oflags, int in_fd, int out_fd) >> >> This is getting rather wierd as a signature. >> >> If O_RDONLY, then in_fd is ignored, 'fd' is input. >> >> If O_WRONLY, then out_fd is ignored, 'fd' is output >> >> What about instead simply : >> >> runIO(const char *srcpath, int srcfd, >> const char *dstpath, int dstfd) >> >> so there's no read vs write distinction at all. > > maybe I am a bit confused/tired, but I don't see how this would work, > which side one of those is the disk, where we want to check for S_ISBLK and O_DIRECT, and buffer accordingly? We call fstat on the FD, we'll know which FD is a pipe/socket vs which FD is a file/blockdev. If we call fcntl(GET_FL) we can also discover if O_DIRECT is turned on or not.