Re: [libvirt] [PATCH V6 3/3] Add support for file descriptor sets
On 02/15/2013 10:01 PM, Eric Blake wrote:
On 02/14/2013 05:00 AM, Stefan Berger wrote:
>
>
> +static char *
> +qemuCommandPrintFDSet(int fdset, int fd, int open_flags, const char *name)
> +{
> + const char *mode = "";
> + virBuffer buf = VIR_BUFFER_INITIALIZER;
> +
> + if (name) {
> + switch ((open_flags & O_ACCMODE)) {
> + case O_RDONLY:
> + mode = "RDONLY:";
> + break;
> + case O_WRONLY:
> + mode = "WRONLY:";
> + break;
> + case O_RDWR:
> + mode = "RDWR:";
> + break;
Is it worth a default case when the mode is unrecognized? Then again,
unless the Linux kernel ever gains O_SEARCH/O_EXEC support, there
probably won't ever be any code hitting the default case.
Then we can leave it as-is I suppose. We can always treat other flags
separately in this case statement if needed in the future.
> + }
> + }
> +
> + virBufferAsprintf(&buf, "set=%d,fd=%d%s%s", fdset, fd,
> + (name) ? ",opaque=" : "",
> + mode);
> + if (name)
> + virBufferEscape(&buf, ',', ",", "%s",
name);
Slightly easier to read as:
virBufferAsprintf(&buf, "set=%d,fd=%d", fdset, fd);
if (name)
virBufferEscape(&buf, ',', ",", ",opaque=%s", name);
Something like this, yes. 'mode' still needs to be printed in the
if(name) part but cannot be part of virBufferEscape.
Rather than having the user supply a sentinel, would it be better to
have the user provide nopenFlags? That is, when opening a single fd,
passing '&mode, 1' is easier than passing 'int[] { mode, -1}',
especially if we don't want to use C99 initializer syntax. For that
matter, would it be any easier to pass a flags instead of a mode, where
we have the bitwise-or of:
QEMU_USE_RDONLY = 1 << 0, // O_RDONLY
QEMU_USE_RDWR = 1 << 1, // O_RDWR
QEMU_USE WRONLY = 1 << 2, // O_WRONLY
on the grounds that writing 'QEMU_USE_RDONLY | QEMU_USE_RDWR' looks a
little cleaner than writing '(int[]){O_RDONLY, O_RDWR, -1}' (no
temporary arrays required).
For that we would need additional code everywhere where we need to
convert these QEMU_USE_* to the POSIX flags by bitwise sampling the
flags in a loop,which is practically everywhere where the POSIX flags
are understood today, e.g., qemuOpenFile(). I am not sure it will make
things easier.
Stefan