driver.storage.fdtable¶

Per-process file descriptor table management.

Overview¶

Each process owns one TFDTable, allocated at process creation and freed when the process is reaped. The table holds up to MAX_FDS (64) file descriptor slots. File handles are 1-based indices into this table; handle 0 is always invalid.

The VFS layer calls fd_alloc, fd_get, and fd_close rather than manipulating the table directly. This unit has no knowledge of VFS paths or filesystem drivers — it only manages slot lifetime, string ownership, and pre-loaded data buffers stored in each descriptor.

Dependencies¶

memory.heap
driver.storage.types
core.util, arch.x86.util

Constants¶

MAX_FDS¶

64 — Maximum number of file descriptors a single process may have open simultaneously.

Types¶

TFileDescriptor / PFileDescriptor¶

One slot in the per-process FD table.

Field	Type	Description
`InUse`	`boolean`	True if this slot is allocated
`Volume`	`PStorage_Volume`	Volume the file resides on
`Directory`	`pchar`	Directory path within the volume (heap-owned)
`FileName`	`pchar`	Filename within that directory (heap-owned)
`OpenMode`	`uint8`	`TOpenMode` ordinal (avoids circular VFS type dependency)
`WriteMode`	`uint8`	`TWriteMode` ordinal
`DataBuffer`	`puint32`	Pre-loaded file data for small files, nil otherwise
`DataSize`	`uint32`	Size of pre-loaded data in bytes
`Loaded`	`boolean`	True if data has been pre-loaded into `DataBuffer`
`StreamOff`	`uint32`	Current byte offset for streaming / on-demand reads

TFDTable / PFDTable¶

Fixed-size array of MAX_FDS file descriptor slots. One instance per process.

Functions and Procedures¶

fd_table_new¶

function fd_table_new : PFDTable;

Allocates and zero-initialises a new FD table on the heap. Called once per process at creation time. Returns nil on allocation failure.

fd_table_free¶

procedure fd_table_free(table : PFDTable);

Closes all open descriptors in the table via fd_close_all, then frees the table itself. Safe to call with nil.

fd_alloc¶

function fd_alloc(table : PFDTable) : uint32;

Finds the first free slot in the table and returns its 1-based handle. Returns 0 if the table is full or nil. Does not mark the slot as in-use; the caller must set InUse := true after populating the descriptor fields.

fd_get¶

function fd_get(table : PFDTable; handle : uint32) : PFileDescriptor;

Returns a pointer to the descriptor for the given 1-based handle. Returns nil if the handle is out of range (0 or > MAX_FDS) or if the slot is not marked InUse.

fd_close¶

function fd_close(table : PFDTable; handle : uint32) : boolean;

Closes a single file descriptor: frees DataBuffer, Directory, and FileName strings, zeroes tracking fields, and marks the slot as not in-use. Returns true if the handle was valid and open, false otherwise.

fd_close_all¶

procedure fd_close_all(table : PFDTable);

Iterates all slots and closes every in-use descriptor. Used during process cleanup before the table itself is freed.

Notes¶

Handles are 1-based so that 0 can serve as a sentinel "invalid handle" value throughout the kernel.
The fd_free_entry internal procedure performs the actual resource release; it is called by both fd_close and fd_close_all.
DataBuffer is only populated for pre-loaded files (e.g., files opened in omReadOnly or omReadWrite mode). Stream-mode handles leave it nil and use StreamOff for incremental reads.