zfs_file: implement zfs_file_deallocate for FreeBSD 14

FreeBSD 14 gained a `VOP_DEALLOCATE` VFS operation and a `fspacectl`
syscall to use it. At minimum, these zero the given region, and if the
underlying filesystem supports it, can make the region sparse. We can
use this to get TRIM-like behaviour for file vdevs.

Sponsored-by: https://despairlabs.com/sponsor/
Signed-off-by: Rob Norris <[email protected]>

Author: robn

lib/libzpool/kernel.c

@@ -1380,6 +1380,12 @@ zfs_file_deallocate(zfs_file_t *fp, loff_t offset, loff_t len)
 #if defined(__linux__)
 	rc = fallocate(fp->f_fd,
 	    FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE, offset, len);
+#elif defined(__FreeBSD__) && (__FreeBSD_version >= 1400029)
+	struct spacectl_range rqsr = {
+		.r_offset = offset,
+		.r_len = len,
+	};
+	rc = fspacectl(fp->f_fd, SPACECTL_DEALLOC, &rqsr, 0, &rqsr);
 #else
 	(void) fp, (void) offset, (void) len;
 	rc = EOPNOTSUPP;

module/os/freebsd/zfs/zfs_file_os.c

@@ -295,8 +295,20 @@ zfs_file_fsync(zfs_file_t *fp, int flags)
 int
 zfs_file_deallocate(zfs_file_t *fp, loff_t offset, loff_t len)
 {
+	int rc;
+#if __FreeBSD_version >= 1400029
+	struct thread *td;
+
+	td = curthread;
+	rc = fo_fspacectl(fp, SPACECTL_DEALLOC, &offset, &len, 0,
+	    td->td_ucred, td);
+#else
 	(void) fp, (void) offset, (void) len;
-	return (SET_ERROR(EOPNOTSUPP));
+	rc = EOPNOTSUPP;
+#endif
+	if (rc)
+		return (SET_ERROR(rc));
+	return (0);
 }
 
 zfs_file_t *