Enhance f_read() to find the maximum contiguous set of clusters to read, and read it all at once (which is fast) rather one by one (which is slow).
Signed-off-by: Stephen Warren swarren@wwwdotorg.org --- V3: New patch. --- fs/fat/ff.c | 45 ++++++++++++++++++++++++++++++++------------- 1 file changed, 32 insertions(+), 13 deletions(-)
diff --git a/fs/fat/ff.c b/fs/fat/ff.c index 478daa7d6b0b..0df5a9ddcf7c 100644 --- a/fs/fat/ff.c +++ b/fs/fat/ff.c @@ -2593,7 +2593,7 @@ FRESULT f_read ( ) { FRESULT res; - DWORD clst, sect, remain; + DWORD clst, sect, remain, cfptr, cclst, maxclust; UINT rcnt, cc; BYTE csect, *rbuff = (BYTE*)buff;
@@ -2614,27 +2614,46 @@ FRESULT f_read ( if ((fp->fptr % SS(fp->fs)) == 0) { /* On the sector boundary? */ csect = (BYTE)(fp->fptr / SS(fp->fs) & (fp->fs->csize - 1)); /* Sector offset in the cluster */ if (!csect) { /* On the cluster boundary? */ - if (fp->fptr == 0) { /* On the top of the file? */ - clst = fp->sclust; /* Follow from the origin */ - } else { /* Middle or end of the file */ + maxclust = 0; + cfptr = fp->fptr; + cclst = fp->clust; + for (;;) { + if (cfptr == 0) { /* On the top of the file? */ + clst = fp->sclust; /* Follow from the origin */ + } else { /* Middle or end of the file */ #if _USE_FASTSEEK - if (fp->cltbl) - clst = clmt_clust(fp, fp->fptr); /* Get cluster# from the CLMT */ - else + if (fp->cltbl) + clst = clmt_clust(fp, cfptr); /* Get cluster# from the CLMT */ + else #endif - clst = get_fat(fp->fs, fp->clust); /* Follow cluster chain on the FAT */ + clst = get_fat(fp->fs, cclst); /* Follow cluster chain on the FAT */ + } + if (clst < 2) ABORT(fp->fs, FR_INT_ERR); + if (clst == 0xFFFFFFFF) ABORT(fp->fs, FR_DISK_ERR); + if (!maxclust) { + fp->clust = clst; /* Update current cluster */ + } else { + if (clst != (cclst + 1)) + break; + } + maxclust++; + if ((maxclust * fp->fs->csize * SS(fp->fs)) >= btr) + break; + cclst = clst; + cfptr += fp->fs->csize * SS(fp->fs); } - if (clst < 2) ABORT(fp->fs, FR_INT_ERR); - if (clst == 0xFFFFFFFF) ABORT(fp->fs, FR_DISK_ERR); - fp->clust = clst; /* Update current cluster */ + } else { + maxclust = 1; } sect = clust2sect(fp->fs, fp->clust); /* Get current sector */ + if (maxclust > 1) + fp->clust += (maxclust - 1); if (!sect) ABORT(fp->fs, FR_INT_ERR); sect += csect; cc = btr / SS(fp->fs); /* When remaining bytes >= sector size, */ if (cc) { /* Read maximum contiguous sectors directly */ - if (csect + cc > fp->fs->csize) /* Clip at cluster boundary */ - cc = fp->fs->csize - csect; + if (csect + cc > (fp->fs->csize * maxclust)) /* Clip at cluster boundary */ + cc = (fp->fs->csize * maxclust) - csect; if (disk_read(fp->fs->drv, rbuff, sect, cc) != RES_OK) ABORT(fp->fs, FR_DISK_ERR); #if !_FS_READONLY && _FS_MINIMIZE <= 2 /* Replace one of the read sectors with cached data if it contains a dirty sector */