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[/] [or1k_old/] [trunk/] [uclinux/] [uClinux-2.0.x/] [fs/] [fat/] [buffer.c] - Blame information for rev 1782

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1 199 simons 
/*
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 * linux/fs/fat/buffer.c
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 *
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 *
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 */
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#include <linux/mm.h>
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#include <linux/malloc.h>
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#include <linux/string.h>
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#include <linux/fs.h>
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#include <linux/msdos_fs.h>
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#if 0
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#  define PRINTK(x) printk x
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#else
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#  define PRINTK(x)
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#endif
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struct buffer_head *fat_bread (
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        struct super_block *sb,
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        int block)
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{
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        struct buffer_head *ret = NULL;
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        PRINTK(("fat_bread: block=0x%x\n", block));
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        /* Note that the blocksize is 512 or 1024, but the first read
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           is always of size 1024. Doing readahead may be counterproductive
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           or just plain wrong. */
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        if (sb->s_blocksize == 512) {
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                ret = bread (sb->s_dev,block,512);
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        } else {
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                struct buffer_head *real = bread (sb->s_dev,block>>1,1024);
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                if (real != NULL){
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                        ret = (struct buffer_head *)
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                          kmalloc (sizeof(struct buffer_head), GFP_KERNEL);
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                        if (ret != NULL) {
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                                /* #Specification: msdos / strategy / special device / dummy blocks
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                                        Many special device (Scsi optical disk for one) use
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                                        larger hardware sector size. This allows for higher
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                                        capacity.
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                                        Most of the time, the MsDOS file system that sit
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                                        on this device is totally unaligned. It use logically
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                                        512 bytes sector size, with logical sector starting
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                                        in the middle of a hardware block. The bad news is
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                                        that a hardware sector may hold data own by two
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                                        different files. This means that the hardware sector
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                                        must be read, patch and written almost all the time.
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                                        Needless to say that it kills write performance
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                                        on all OS.
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                                        Internally the linux msdos fs is using 512 bytes
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                                        logical sector. When accessing such a device, we
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                                        allocate dummy buffer cache blocks, that we stuff
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                                        with the information of a real one (1k large).
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                                        This strategy is used to hide this difference to
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                                        the core of the msdos fs. The slowdown is not
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                                        hidden though!
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                                */
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                                /*
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                                        The memset is there only to catch errors. The msdos
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                                        fs is only using b_data
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                                */
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                                memset (ret,0,sizeof(*ret));
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                                ret->b_data = real->b_data;
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                                if (block & 1) ret->b_data += 512;
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                                ret->b_next = real;
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                        }else{
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                                brelse (real);
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                        }
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                }
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        }
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        return ret;
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}
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struct buffer_head *fat_getblk (
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        struct super_block *sb,
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        int block)
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{
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        struct buffer_head *ret = NULL;
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        PRINTK(("fat_getblk: block=0x%x\n", block));
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        if (sb->s_blocksize == 512){
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                ret = getblk (sb->s_dev,block,512);
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        }else{
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                /* #Specification: msdos / special device / writing
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                        A write is always preceded by a read of the complete block
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                        (large hardware sector size). This defeat write performance.
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                        There is a possibility to optimize this when writing large
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                        chunk by making sure we are filling large block. Volunteer ?
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                */
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                ret = fat_bread (sb,block);
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        }
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        return ret;
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}
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void fat_brelse (
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        struct super_block *sb,
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        struct buffer_head *bh)
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{
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        if (bh != NULL){
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                if (sb->s_blocksize == 512){
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                        brelse (bh);
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                }else{
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                        brelse (bh->b_next);
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                        /* We can free the dummy because a new one is allocated at
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                                each fat_getblk() and fat_bread().
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                        */
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                        kfree (bh);
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                }
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        }
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}
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void fat_mark_buffer_dirty (
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        struct super_block *sb,
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        struct buffer_head *bh,
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        int dirty_val)
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{
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        if (sb->s_blocksize != 512){
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                bh = bh->b_next;
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        }
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        mark_buffer_dirty (bh,dirty_val);
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}
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void fat_set_uptodate (
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        struct super_block *sb,
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        struct buffer_head *bh,
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        int val)
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{
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        if (sb->s_blocksize != 512){
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                bh = bh->b_next;
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        }
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        mark_buffer_uptodate(bh, val);
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}
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int fat_is_uptodate (
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        struct super_block *sb,
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        struct buffer_head *bh)
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{
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        if (sb->s_blocksize != 512){
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                bh = bh->b_next;
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        }
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        return buffer_uptodate(bh);
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}
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void fat_ll_rw_block (
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        struct super_block *sb,
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        int opr,
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        int nbreq,
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        struct buffer_head *bh[32])
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{
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        if (sb->s_blocksize == 512){
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                ll_rw_block(opr,nbreq,bh);
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        }else{
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                struct buffer_head *tmp[32];
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                int i;
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                for (i=0; i<nbreq; i++){
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                        tmp[i] = bh[i]->b_next;
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                }
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                ll_rw_block(opr,nbreq,tmp);
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        }
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}
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