buffer.c

从大量的wince源代码中剥离出的fat文件系统源代码.移植性非常高. 里面带有source i.rar

        if (cBufVolumes++ == 0) {

            DWORD cbTotal;
            PBYTE pbCarve = NULL;

            if (cbufTotal == 0) {

                SYSTEM_INFO si;

                InitList((PDLINK)&dlBufMRU);

                // Determine buffer size (and number of blocks per that size)

                GetSystemInfo(&si);

#ifdef BIG_BUFFERS
                cbBuf = si.dwPageSize;

                // Make sure that a system with, say, 4K pages will still work
                // with a device that has, say, 8K sectors.

                if (cbBuf < pvol->v_pdsk->d_diActive.di_bytes_per_sect) {
                    cbBuf = pvol->v_pdsk->d_diActive.di_bytes_per_sect;
                    flBuf |= GBUF_LOCALALLOC;
                }
#else
                cbBuf = pvol->v_pdsk->d_diActive.di_bytes_per_sect;

                if (cbBuf != si.dwPageSize)
                    flBuf |= GBUF_LOCALALLOC;
#endif
                // Make sure the optimal buffer size for this volume is
                // ALSO at least as large as our block size.

                if (cbBuf < BLOCK_SIZE)
                    cbBuf = BLOCK_SIZE;

                // Make sure buffer size is a multiple of the block size.

                if ((cbBuf & BLOCK_OFFSET_MASK) != 0) {
                    DEBUGMSG(ZONE_INIT || ZONE_ERRORS,(DBGTEXT("FATFS!AllocBufferPool: cbBuf(%d) not a multiple of BLOCK_SIZE(%d), failing...\n"), cbBuf, BLOCK_SIZE));
                    goto error;
                }

                // Calculate the number of blocks per buffer.

                cblkBuf = cbBuf >> BLOCK_LOG2;

                // Calculate mask that converts a block into a buffer-granular block.

                maskBufBlock = ~(cblkBuf-1);

                // Make sure number of blocks per buffer is power of 2.

                if ((cblkBuf & ~maskBufBlock) != 0) {
                    DEBUGMSG(ZONE_INIT || ZONE_ERRORS,(DBGTEXT("FATFS!AllocBufferPool: cblkBuf(%d) is not a power of two, failing...\n"), cblkBuf));
                    goto error;
                }

                // See if it makes sense to allocate a large chunk of virtual
                // memory and carve it up (ie, if the total size of the buffer
                // pool is a perfect number of pages).

                ASSERT(pbBufCarve == NULL);

                if ((cbTotal = DEF_BUFFERS * cbBuf) % si.dwPageSize == 0) {

                    pbBufCarve = VirtualAlloc(0,
                                              cbTotal,
                                              MEM_RESERVE|MEM_COMMIT,
                                            //MEM_RESERVE|MEM_MAPPED,
                                              PAGE_READWRITE
                                            //PAGE_NOACCESS
                                             );
                    if (pbBufCarve) {
                        DEBUGALLOC(cbTotal);
                        pbCarve = pbBufCarve;
                    }
                }
            }

            while (cbufTotal < DEF_BUFFERS) {
                PBUF pbuf;
                if (!(pbuf = NewBuffer(cbBuf, &pbCarve)))
                    break;
                cbufTotal++;
                AddItem((PDLINK)&dlBufMRU, (PDLINK)&pbuf->b_dlink);
            }

            if (cbufTotal < MIN_BUFFERS) {

              error:
                FreeBufferPool(pvol);
                LeaveCriticalSection(&csBuffers);
                return FALSE;
            }

            // Since we have at least MIN_BUFFERS buffers now, calculate
            // the number of threads our buffer pool can handle simultaneously.
            // If DEMAND_PAGING is enabled, we reduce that number by 1 so that
            // a Pagein thread can always assume there are adequate buffers.

#ifdef DEMAND_PAGING
            cBufThreads = cBufThreadsOrig = cbufTotal / MIN_BUFFERS - 1;
#else
            cBufThreads = cBufThreadsOrig = cbufTotal / MIN_BUFFERS;
#endif
        }
    }

    // For all calls (first time or not), we must invalidate any buffers
    // we retained for an unmounted volume that was subsequently *recycled*
    // instead of *remounted*.

    if (pvol->v_flags & VOLF_RECYCLED)
        InvalidateBufferSet(pvol, TRUE);

    LeaveCriticalSection(&csBuffers);
    return TRUE;
}


/*  FreeBufferPool - free all buffers in buffer pool
 *
 *  ENTRY
 *      pvol - pointer to VOLUME currently being unmounted
 *
 *  EXIT
 *      TRUE if volume can be freed, or FALSE if not (ie, there are still
 *      dirty buffers that could not be committed).  Note that if the volume
 *      wasn't going to be freed to begin with, we always return FALSE.
 *
 *      This module keeps track of the number of buffer clients (volumes),
 *      and only when the last client has called FreeBufferPool will the pool
 *      actually be freed (subject to all buffers being clean, of course).
 */

BOOL FreeBufferPool(PVOLUME pvol)
{
    PBUF pbuf, pbufEnd;
    BOOL fFree = TRUE;
    BOOL fFreeCarve = FALSE;

    ASSERT(OWNCRITICALSECTION(&pvol->v_cs));

    // If the current volume isn't even using the buffer pool (yet),
    // then we're done.

    if (!(pvol->v_flags & VOLF_BUFFERED))
        return fFree;

    EnterCriticalSection(&csBuffers);

    // This is our last chance to commit all dirty buffers.  With any
    // luck, this will clean all the buffers, allowing us to free them all.
    // That will be our assumption at least.  If dirty buffers still remain
    // for this volume, its DIRTY bit will get set again, below.

    CommitVolumeBuffers(pvol);
    pvol->v_flags &= ~VOLF_DIRTY;

    // If we have buffers carved from a single chunk of memory, then
    // quickly walk the entire list and determine if ALL the carved buffers
    // can be freed.  A single dirty or held carved buffer means that NONE
    // of the carved buffers can be freed.

    pbuf = dlBufMRU.pbufNext;
    pbufEnd = (PBUF)&dlBufMRU;

    if (pbBufCarve) {
        if (cBufVolumes == 1) {
            fFreeCarve = TRUE;
            if (!(pvol->v_flags & VOLF_CLOSING)) {
                while (pbuf != pbufEnd) {
                    if ((pbuf->b_flags & BUF_DIRTY) || HeldBuffer(pbuf)) {
                        DEBUGMSG(TRUE,(DBGTEXT("FATFS!FreeBufferPool: dirty/held buffer for block %d!\n"), pbuf->b_blk));
                        if (pbuf->b_flags & BUF_CARVED) {
                            fFreeCarve = fFree = FALSE;
#ifndef DEBUG
                            break;  // in debug builds, we like to see all the dirty buffers
#endif
                        }
                    }
                    pbuf = pbuf->b_dlink.pbufNext;
                }
            }
        }
        if (fFreeCarve) {
            DEBUGFREE(DEF_BUFFERS * cbBuf);
            VERIFYTRUE(VirtualFree(pbBufCarve, 0, MEM_RELEASE));
            pbBufCarve = NULL;
        }
    }

    // Now walk the buffer list again, freeing every buffer that we can.

    pbuf = dlBufMRU.pbufNext;

    while (pbuf != pbufEnd) {

        BOOL fClean = !(pbuf->b_flags & BUF_DIRTY) && !HeldBuffer(pbuf);

        if (pvol->v_flags & VOLF_CLOSING) {

            // The only reason we hold the buffer is so that CleanBuffer
            // won't generate a bogus assertion.  We don't care about the
            // data anymore, so it is otherwise pointless.

            HoldBuffer(pbuf);
            CleanBuffer(pbuf);
            UnholdBuffer(pbuf);

            fClean = TRUE;
        }

        if (cBufVolumes > 1) {

            // If there are still other clients (ie, volumes), then all we
            // want to do is remove any buffer references to this volume
            // if it's being destroyed, so that we avoid false matches
            // if another volume with the same address gets allocated later.

            if (pbuf->b_pvol == pvol) {
                if (fClean) {
                    pbuf->b_pvol = NULL;
                } else {
                    pvol->v_flags |= VOLF_DIRTY;
                    fFree = FALSE;
                }
            }
        }
        else {

            ASSERT(pbuf->b_pvol == NULL || pbuf->b_pvol == pvol);

            if (fClean) {

                pbuf->b_pvol = NULL;

                // The current buffer is clean.  Now, if this is NOT a carved
                // buffer, or it is but we can free all the carved buffers anyway,
                // then free the current buffer.

                if (!(pbuf->b_flags & BUF_CARVED) || fFreeCarve) {

                    cbufTotal--;

                    if (!(pbuf->b_flags & BUF_CARVED)) {
                        DEBUGFREE(cbBuf);
                        if (flBuf & GBUF_LOCALALLOC)
                            VERIFYNULL(LocalFree((HLOCAL)pbuf->b_pdata));
                        else
                            VERIFYTRUE(VirtualFree(pbuf->b_pdata, 0, MEM_RELEASE));
                    }

                    RemoveItem((PDLINK)&pbuf->b_dlink);

                    DEBUGFREE(sizeof(BUF));
                    VERIFYNULL(LocalFree((HLOCAL)pbuf));

                    pbuf = dlBufMRU.pbufNext;
                    continue;
                }
            }
            else {
                ASSERT(pbuf->b_pvol == pvol);

                pvol->v_flags |= VOLF_DIRTY;
                fFree = FALSE;
            }
        }
        pbuf = pbuf->b_dlink.pbufNext;
    }

  //DEBUGMSG(cbufTotal, (DBGTEXT("FATFS!FreeBufferPool: %d buffers retained\n"), cbufTotal));

    // If there were no dirty buffers for this volume, then we can remove
    // its reference to buffer pool.

    if (!(pvol->v_flags & VOLF_DIRTY)) {
        pvol->v_flags &= ~VOLF_BUFFERED;
        cBufVolumes--;
    }

    LeaveCriticalSection(&csBuffers);

    return fFree;
}


/*  ModifyBuffer - Prepare to dirty buffer
 *
 *  ENTRY
 *      pbuf - pointer to buffer
 *      pMod - pointer to modification
 *      cbMod - length of modification (ZERO to prevent logging)
 *
 *  EXIT
 *      ERROR_SUCCESS if the buffer is allowed to be modified, otherwise
 *      some error code (eg, ERROR_WRITE_PROTECT).
 */

DWORD ModifyBuffer(PBUF pbuf, PVOID pMod, int cbMod)
{
    DWORD dwError = ERROR_SUCCESS;

    ASSERTHELDBUFFER(pbuf);

    if (pbuf->b_pvol->v_flags & VOLF_READONLY) {
        dwError = ERROR_WRITE_PROTECT;
    }

    if (!dwError)
        DirtyBuffer(pbuf);

    return dwError;
}


/*  DirtyBuffer - Dirty a buffer
 *
 *  ENTRY
 *      pbuf - pointer to BUF
 *
 *  EXIT
 *      The buffer is marked DIRTY.
 */

void DirtyBuffer(PBUF pbuf)
{
    ASSERTHELDBUFFER(pbuf);

    pbuf->b_flags |= BUF_DIRTY;
}


/*  DirtyBufferError - Dirty a buffer that cannot be cleaned
 *
 *  ENTRY
 *      pbuf - pointer to BUF
 *      pMod - pointer to modification (NULL if none)
 *      cbMod - length of modification (ZERO if none)
 *
 *  EXIT
 *      The buffer is marked DIRTY, and any error is recorded.
 */

void DirtyBufferError(PBUF pbuf, PVOID pMod, int cbMod)
{
    ASSERTHELDBUFFER(pbuf);

    pbuf->b_flags |= BUF_DIRTY;

    EnterCriticalSection(&csBuffers);

    if (!(pbuf->b_flags & BUF_ERROR)) {
        if (cbufError % MIN_BUFFERS == 0)
            InterlockedDecrement(&cBufThreads);
        cbufError++;
        pbuf->b_flags |= BUF_ERROR;
    }
    LeaveCriticalSection(&csBuffers);
}


/*  CommitBuffer - Commit a dirty buffer
 *
 *  ENTRY
 *      pbuf - pointer to BUF
 *      fCS - TRUE if csBuffers is held, FALSE if not
 *
 *  EXIT
 *      ERROR_SUCCESS (0) if successful, non-zero if not.
 *
 *  NOTES
 *      Since we clear BUF_DIRTY before calling WriteVolume, it's important
 *      we do something to prevent FindBuffer from getting any bright ideas
 *      about reusing it before we have finished writing the original dirty
 *      contents.  Furthermore, since we don't want to hold csBuffers across
 *      the potentially lengthy WriteVolume request, applying another hold to
 *      the buffer is really our only option.
 */

DWORD CommitBuffer(PBUF pbuf, BOOL fCS)
{
    PBYTE pbMod = NULL;
    int cbMod = 0;
    DWORD dwError = ERROR_SUCCESS;

#ifdef UNDER_CE 
    ASSERT(fCS == OWNCRITICALSECTION(&csBuffers));