On Wed, Jun 26, 2019 at 04:37:23PM +0800, Anand Jain wrote:
> This sets the readmirror=<parm> as a btrfs.<attr> extentded attribute.
>
> Signed-off-by: Anand Jain <anand.jain@xxxxxxxxxx>
> ---
> props.c | 49 +++++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 49 insertions(+)
>
> diff --git a/props.c b/props.c
> index 3a498bd9e904..1d1a2c7f9d14 100644
> --- a/props.c
> +++ b/props.c
> @@ -178,6 +178,53 @@ out:
> return ret;
> }
>
> +static int prop_readmirror(enum prop_object_type type, const char *object,
> + const char *name, const char *value)
> +{
> + int fd;
> + int ret;
> + char buf[256] = {0};
> + char *xattr_name;
> + DIR *dirstream = NULL;
> +
> + fd = open_file_or_dir3(object, &dirstream, value ? O_RDWR : O_RDONLY);
> + if (fd < 0) {
> + ret = -errno;
> + error("failed to open %s: %m", object);
> + return ret;
> + }
> +
> + xattr_name = alloc_xattr_name(name);
> + if (IS_ERR(xattr_name)) {
> + error("failed to alloc xattr_name %s: %m", object);
> + return PTR_ERR(xattr_name);
> + }
> +
> + ret = 0;
> + if (value) {
> + if (fsetxattr(fd, xattr_name, value, strlen(value), 0) < 0) {
> + ret = -errno;
> + error("failed to set readmirror for %s: %m", object);
> + }
> + } else {
> + if (fgetxattr(fd, xattr_name, buf, 256) < 0) {
> + if (errno != ENOATTR) {
> + ret = -errno;
> + error("failed to get readmirror for %s: %m",
> + object);
> + }
> + } else {
> + fprintf(stdout, "readmirror=%.*s\n", (int) strlen(buf),
> + buf);
> + }
> + }
> +
> + free(xattr_name);
> + close_file_or_dir(fd, dirstream);
> +
> + return ret;
> +}
> +
> const struct prop_handler prop_handlers[] = {
> {"ro", "Set/get read-only flag of subvolume.", 0, prop_object_subvol,
> prop_read_only},
> @@ -185,5 +232,7 @@ const struct prop_handler prop_handlers[] = {
> prop_object_dev | prop_object_root, prop_label},
> {"compression", "Set/get compression for a file or directory", 0,
> prop_object_inode, prop_compression},
> + {"readmirror", "set/get readmirror policy for filesystem", 0,
> + prop_object_root, prop_readmirror},
For some unknown reason the object type for filesystem-wide props is
called prop_object_root, which is correct, but it got me confused first.
So the most reliable way to set it is
$ btrfs prop set -t filesystem /path readmirror <VALUE>
and
$ btrfs prop set /path readmirror <VALUE>
will auto-detect the object type by /path, but I'm not sure what exactly
does it do in case it's a mount point but not the toplevel subvolume.
