+/* llapi_layout user interface */
+
+/** Opaque data type abstracting the layout of a Lustre file. */
+struct llapi_layout;
+
+/*
+ * Flags to control how layouts are retrieved.
+ */
+
+/* Replace non-specified values with expected inherited values. */
+#define LAYOUT_GET_EXPECTED 0x1
+
+/**
+ * Return a pointer to a newly-allocated opaque data structure containing
+ * the layout for the file at \a path. The pointer should be freed with
+ * llapi_layout_free() when it is no longer needed. Failure is indicated
+ * by a NULL return value and an appropriate error code stored in errno.
+ */
+struct llapi_layout *llapi_layout_get_by_path(const char *path, uint32_t flags);
+
+/**
+ * Return a pointer to a newly-allocated opaque data type containing the
+ * layout for the file referenced by open file descriptor \a fd. The
+ * pointer should be freed with llapi_layout_free() when it is no longer
+ * needed. Failure is indicated by a NULL return value and an
+ * appropriate error code stored in errno.
+ */
+struct llapi_layout *llapi_layout_get_by_fd(int fd, uint32_t flags);
+
+/**
+ * Return a pointer to a newly-allocated opaque data type containing the
+ * layout for the file associated with Lustre file identifier string
+ * \a fidstr. The string \a path must name a path within the
+ * filesystem that contains the file being looked up, such as the
+ * filesystem root. The returned pointer should be freed with
+ * llapi_layout_free() when it is no longer needed. Failure is
+ * indicated with a NULL return value and an appropriate error code
+ * stored in errno.
+ */
+struct llapi_layout *llapi_layout_get_by_fid(const char *path,
+ const lustre_fid *fid,
+ uint32_t flags);
+
+/**
+ * Allocate a new layout. Use this when creating a new file with
+ * llapi_layout_file_create().
+ */
+struct llapi_layout *llapi_layout_alloc(void);
+
+/**
+ * Free memory allocated for \a layout.
+ */
+void llapi_layout_free(struct llapi_layout *layout);
+
+/** Not a valid stripe size, offset, or RAID pattern. */
+#define LLAPI_LAYOUT_INVALID 0x1000000000000001ULL
+
+/**
+ * When specified or returned as the value for stripe count,
+ * stripe size, offset, or RAID pattern, the filesystem-wide
+ * default behavior will apply.
+ */
+#define LLAPI_LAYOUT_DEFAULT (LLAPI_LAYOUT_INVALID + 1)
+
+/**
+ * When specified or returned as the value for stripe count, all
+ * available OSTs will be used.
+ */
+#define LLAPI_LAYOUT_WIDE (LLAPI_LAYOUT_INVALID + 2)
+
+/**
+ * When specified as the value for layout pattern, file objects will be
+ * stored using RAID0. That is, data will be split evenly and without
+ * redundancy across all OSTs in the layout.
+ */
+#define LLAPI_LAYOUT_RAID0 0
+
+/**
+ * Flags to modify how layouts are retrieved.
+ */
+/******************** Stripe Count ********************/
+
+/**
+ * Store the stripe count of \a layout in \a count.
+ *
+ * \retval 0 Success
+ * \retval -1 Error with status code in errno.
+ */
+int llapi_layout_stripe_count_get(const struct llapi_layout *layout,
+ uint64_t *count);
+
+/**
+ * Set the stripe count of \a layout to \a count.
+ *
+ * \retval 0 Success.
+ * \retval -1 Invalid argument, errno set to EINVAL.
+ */
+int llapi_layout_stripe_count_set(struct llapi_layout *layout, uint64_t count);
+
+/******************** Stripe Size ********************/
+
+/**
+ * Store the stripe size of \a layout in \a size.
+ *
+ * \retval 0 Success.
+ * \retval -1 Invalid argument, errno set to EINVAL.
+ */
+int llapi_layout_stripe_size_get(const struct llapi_layout *layout,
+ uint64_t *size);
+
+/**
+ * Set the stripe size of \a layout to \a stripe_size.
+ *
+ * \retval 0 Success.
+ * \retval -1 Invalid argument, errno set to EINVAL.
+ */
+int llapi_layout_stripe_size_set(struct llapi_layout *layout, uint64_t size);
+
+/******************** Stripe Pattern ********************/
+
+/**
+ * Store the stripe pattern of \a layout in \a pattern.
+ *
+ * \retval 0 Success.
+ * \retval -1 Error with status code in errno.
+ */
+int llapi_layout_pattern_get(const struct llapi_layout *layout,
+ uint64_t *pattern);
+
+/**
+ * Set the stripe pattern of \a layout to \a pattern.
+ *
+ * \retval 0 Success.
+ * \retval -1 Invalid argument, errno set to EINVAL.
+ */
+int llapi_layout_pattern_set(struct llapi_layout *layout, uint64_t pattern);
+
+/******************** OST Index ********************/
+
+/**
+ * Store the index of the OST where stripe number \a stripe_number is stored
+ * in \a index.
+ *
+ * An error return value will result from a NULL layout, if \a
+ * stripe_number is out of range, or if \a layout was not initialized
+ * with llapi_layout_lookup_by{path,fd,fid}().
+ *
+ * \retval 0 Success
+ * \retval -1 Invalid argument, errno set to EINVAL.
+ */
+int llapi_layout_ost_index_get(const struct llapi_layout *layout,
+ uint64_t stripe_number, uint64_t *index);
+
+/**
+ * Set the OST index associated with stripe number \a stripe_number to
+ * \a ost_index.
+ * NB: This is currently supported only for \a stripe_number = 0 and
+ * other usage will return ENOTSUPP in errno. A NULL \a layout or
+ * out-of-range \a stripe_number will return EINVAL in errno.
+ *
+ * \retval 0 Success.
+ * \retval -1 Error with errno set to non-zero value.
+ */
+int llapi_layout_ost_index_set(struct llapi_layout *layout, int stripe_number,
+ uint64_t index);
+
+/******************** Pool Name ********************/
+
+/**
+ * Store up to \a pool_name_len characters of the name of the pool of
+ * OSTs associated with \a layout into the buffer pointed to by
+ * \a pool_name.
+ *
+ * The correct calling form is:
+ *
+ * llapi_layout_pool_name_get(layout, pool_name, sizeof(pool_name));
+ *
+ * A pool defines a set of OSTs from which file objects may be
+ * allocated for a file using \a layout.
+ *
+ * On success, the number of bytes stored is returned, excluding the
+ * terminating '\0' character (zero indicates that \a layout does not
+ * have an associated OST pool). On error, -1 is returned and errno is
+ * set appropriately. Possible sources of error include a NULL pointer
+ * argument or insufficient space in \a dest to store the pool name,
+ * in which cases errno will be set to EINVAL.
+ *
+ * \retval 0+ The number of bytes stored in \a dest.
+ * \retval -1 Invalid argument, errno set to EINVAL.
+ */
+int llapi_layout_pool_name_get(const struct llapi_layout *layout,
+ char *pool_name, size_t pool_name_len);
+
+/**
+ * Set the name of the pool of OSTs from which file objects will be
+ * allocated to \a pool_name.
+ *
+ * If the pool name uses "fsname.pool" notation to qualify the pool name
+ * with a filesystem name, the "fsname." portion will be silently
+ * discarded before storing the value. No validation that \a pool_name
+ * is an existing non-empty pool in filesystem \a fsname will be
+ * performed. Such validation can be performed by the application if
+ * desired using the llapi_search_ost() function. The maximum length of
+ * the stored value is defined by the constant LOV_MAXPOOLNAME.
+ *
+ * \retval 0 Success.
+ * \retval -1 Invalid argument, errno set to EINVAL.
+ */
+int llapi_layout_pool_name_set(struct llapi_layout *layout,
+ const char *pool_name);