LockFileRegions Function Overview

	HRESULT _Must_inspect_result_ _Success_(SUCCEEDED(return)) LockFileRegions(	
		_In_ PFILE_INFO pFileInfo,
		_Inout_ PLOCK_FILE_INFO pLockInfo
	)
	;

The LockFileRegions function attempts to lock one or more byte ranges within a file using the Windows LockFile API. It implements a best-effort, per-region locking strategy rather than an atomic all-or-nothing model. Each region is locked independently, and partial success is allowed.

What It Does

The function receives:

• A FILE_INFO structure containing a valid file handle
• A LOCK_FILE_INFO structure specifying one or more byte ranges to lock

It then attempts to lock each region individually using LockFile.

Key Behavior

No Rollback on Partial Failure

If some regions lock successfully but others fail, the function does not roll back the successful locks. This �fail-open� behavior allows callers to:

• Use any regions that did lock successfully
• Retry failed regions later
• Continue processing with partially locked regions

Successfully locked regions remain locked until explicitly released via UnLockFileRegions.

Operation Flow

1. Input Validation

• pLockInfo must not be NULL
• pFileInfo must be valid
• nLockRegions must not exceed MAX_LOCK_REGIONS

2. Parameter Pre-Check

Before locking begins, the function iterates through all regions:

• Ensures each region has a non-zero lock size
• Initializes bLocked, bLockResult, and bUnlockResult to FALSE

3. Locking Loop

For each region, LockFile is called with the region�s offset and length:

• If lock fails:
  • bLocked = FALSE
  • bLockResult = FALSE
  • Increment uFailedCount
  • Record first error HRESULT
• If lock succeeds:
  • bLocked = TRUE
  • bLockResult = TRUE
  • Increment uLockedCount

4. Return Value

The function returns:

• S_OK � only if all regions locked successfully
• Otherwise � an HRESULT corresponding to the first failure

Callers must inspect bLocked for each region to determine which locks succeeded.

Important Notes

• The function does not unlock failed regions
• Successful locks remain active until UnLockFileRegions is called
• The operation is synchronous and blocking (uses LockFile, not LockFileEx)

	1. Call LockFileRegions() with 3 regions (A, B, C)
	2. Suppose region B fails to lock (maybe it's already locked by another process)
  		 - Region A: bLocked = TRUE (usable)
  		 - Region B: bLocked = FALSE (not locked)
   		- Region C: bLocked = TRUE (usable)
   		- Return value: ERROR_LOCK_VIOLATION
	3. Caller can immediately use regions A and C for file operations
	4. In parallel or later, caller can retry locking region B
	5. When done with regions A and C, call UnLockFileRegions() to release them
	6. Region B remains unlocked (caller skipped its unlock since bLocked = FALSE)