SBUF(5) File Formats Manual SBUF(5)

sbuf — Star-Buffer file format

sbuf is a binary file format for storing data in a 1-dimensional array.

A sbuf file begins with a header of four 64-bits integers. The first integer is a power of two (usually 4096) that defines the size of the memory page in bytes (pagesize) on wich the array is aligned. By aligning the array on pagesize, and depending on system requirements, memory mapping can be used to automatically load/unload the array items on demand (see mmap(2)). The second integer is the size of the array. Finally, the 2 remaining integers store the memory size and the memory alignment of each array element.

Fill bytes follow the file header to align the array to pagesize. The array elements are then listed. Fill bytes are finally added to ensure that the overall file size is a multiple of pagesize.

Data are encoded with respect to the little endian bytes ordering, i.e. least significant bytes are stored first.

The file format is as follows:

⟨sbuf⟩ ::= ⟨pagesize⟩ ⟨size⟩ ⟨szitem⟩ ⟨alitem⟩
⟨padding⟩
⟨list⟩
⟨padding⟩
 
⟨pagesize⟩ ::= uint64_t
⟨size⟩ ::= uint64_t # Number of items stored
⟨szitem⟩ ::= uint64_t # Size of an item in bytes
⟨alitem⟩ ::= uint64_t # Alignement of an item (<= pagesize)
 
⟨list⟩ ::= ⟨element⟩ ...
⟨element⟩ ::= ⟨item⟩ ⟨padding⟩
⟨item⟩ ::= char ...
 
⟨padding⟩ ::= [int8_t ...] # Ensure alignment on pagesize

mmap(2)

October 27, 2023 UNIX