btrfs-progs: add API for selecting tree search support and ioctl

Add wrappers around v1 and v2 of TREE_SEARCH ioctl so it can be
transparently used by code. The structures partially overlap but due to
the buffer size the v2 is offset and also needs a filler to expand the
flexible buffer.

Usage:

- define struct btrfs_tree_search_args, all zeros
- btrfs_tree_search_sk() reads offset of the search key within the
  structures
- btrfs_tree_search_ioctl() detect support and call the highest
  supported ioctl version, v2 has been supported since 3.14 but we want
  to keep backward compatibility
- btrfs_tree_search_data() read data from the buffer previously filled
  by ioctl, a sequence of (search header, data)

Signed-off-by: David Sterba <dsterba@suse.com>

common/fsfeatures.c

@@ -31,6 +31,7 @@
 #include "common/string-utils.h"
 #include "common/sysfs-utils.h"
 #include "common/messages.h"
+#include "common/tree-search.h"
 
 /*
  * Insert a root item for temporary tree root
@@ -680,6 +681,29 @@ int btrfs_check_features(const struct btrfs_mkfs_features *features,
 	return 0;
 }
 
+static bool tree_search_v2_supported = false;
+static bool tree_search_v2_initialized = false;
+
+/*
+ * Call the highest supported TREE_SEARCH ioctl version, autodetect support.
+ */
+int btrfs_tree_search_ioctl(int fd, struct btrfs_tree_search_args *sa)
+{
+	/* On first use check the supported status and save it. */
+	if (!tree_search_v2_initialized) {
+		if (btrfs_tree_search2_ioctl_supported(fd) == 1)
+			tree_search_v2_supported = true;
+		tree_search_v2_initialized = true;
+	}
+	sa->use_v2 = tree_search_v2_supported;
+
+	if (sa->use_v2) {
+		sa->args2.buf_size = BTRFS_TREE_SEARCH_V2_BUF_SIZE;
+		return ioctl(fd, BTRFS_IOC_TREE_SEARCH_V2, &sa->args2);
+	}
+	return ioctl(fd, BTRFS_IOC_TREE_SEARCH, &sa->args1);
+}
+
 /*
  * Check if the BTRFS_IOC_TREE_SEARCH_V2 ioctl is supported on a given
  * filesystem, opened at fd

common/tree-search.h

@@ -0,0 +1,33 @@
+#ifndef __COMMON_TREE_SEARCH_H__
+#define __COMMON_TREE_SEARCH_H__
+
+#include "kernel-shared/uapi/btrfs_tree.h"
+#include "kernel-shared/uapi/btrfs.h"
+
+#define BTRFS_TREE_SEARCH_V2_BUF_SIZE		65536
+
+struct btrfs_tree_search_args {
+	union {
+		struct btrfs_ioctl_search_args args1;
+		struct btrfs_ioctl_search_args_v2 args2;
+		u8 filler[sizeof(struct btrfs_ioctl_search_args_v2) +
+			  BTRFS_TREE_SEARCH_V2_BUF_SIZE];
+	};
+	bool use_v2;
+};
+
+int btrfs_tree_search_ioctl(int fd, struct btrfs_tree_search_args *sa);
+
+static inline struct btrfs_ioctl_search_key *btrfs_tree_search_sk(struct btrfs_tree_search_args *sa)
+{
+	/* Same offset for v1 and v2. */
+	return &sa->args1.key;
+}
+
+static inline void *btrfs_tree_search_data(struct btrfs_tree_search_args *sa, unsigned long offset) {
+	if (sa->use_v2)
+		return (void *)(sa->args2.buf + offset);
+	return (void *)(sa->args1.buf + offset);
+}
+
+#endif