# metadataWriteFrom:startingAt:length:error: Synchronously writes file system metadata from a buffer to the resource. ``` - (BOOL) metadataWriteFrom:(void *) buffer startingAt:(off_t) offset length:(size_t) length error:(NSError **) error; ``` ## Parameters `buffer` A buffer to provide the data. `offset` The offset into the resource from which to start writing. `length` The number of bytes to writing. `error` On return, any error encountered while writing data, or `nil` if no error occurred. ## Return Value A Boolean value indicating whether the metadata write succeeded. ## Discussion This method provides access to the Kernel Buffer Cache, which is the primary system cache for file system metadata. Unlike equivalent kernel APIs, this method doesn’t hold any kernel-level claim to the underlying buffers. For the write to succeed, requests must conform to any transfer requirements of the underlying resource. Disk drives typically require sector (`physicalBlockSize`) addressed operations of one or more sector-aligned offsets. > Important: The Kernel Buffer Cache is keyed by offset alone and doesn’t detect overlapping byte ranges between buffers. As a result, the byte ranges of any two metadata operations must never intersect. All accesses to a given disk region must use the same (offset, length) pair. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)