From df49daf03ffabf37ad83f001942763cf2d727988 Mon Sep 17 00:00:00 2001 From: p9ya4sf57 <2573478641@qq.com> Date: Sun, 26 Jun 2022 18:16:42 +0800 Subject: [PATCH] =?UTF-8?q?=E5=AE=9E=E7=8E=B0getdents=E5=87=BD=E6=95=B0?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit --- buffer.c | 443 +++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 443 insertions(+) create mode 100644 buffer.c diff --git a/buffer.c b/buffer.c new file mode 100644 index 0000000..21ae40f --- /dev/null +++ b/buffer.c @@ -0,0 +1,443 @@ +/* + * linux/fs/buffer.c + * + * (C) 1991 Linus Torvalds + */ + +/* + * 'buffer.c' implements the buffer-cache functions. Race-conditions have + * been avoided by NEVER letting a interrupt change a buffer (except for the + * data, of course), but instead letting the caller do it. NOTE! As interrupts + * can wake up a caller, some cli-sti sequences are needed to check for + * sleep-on-calls. These should be extremely quick, though (I hope). + */ + +/* + * NOTE! There is one discordant note here: checking floppies for + * disk change. This is where it fits best, I think, as it should + * invalidate changed floppy-disk-caches. + */ + +#include + +#include +#include +#include +#include +#include +#include + +#define BUF_MAX 4096 +#define MAX_ARG_PAGES 32 +#define NAME_LEN 14 + +extern void put_super(int dev); +extern void invalidate_inodes(int dev); + +extern int end; +struct buffer_head * start_buffer = (struct buffer_head *) &end; +struct buffer_head * hash_table[NR_HASH]; +static struct buffer_head * free_list; +static struct task_struct * buffer_wait = NULL; +int NR_BUFFERS = 0; + +static inline void wait_on_buffer(struct buffer_head * bh) +{ + cli(); + while (bh->b_lock) + sleep_on(&bh->b_wait); + sti(); +} + +int sys_sync(void) +{ + int i; + struct buffer_head * bh; + + sync_inodes(); /* write out inodes into buffers */ + bh = start_buffer; + for (i=0 ; ib_dirt) + ll_rw_block(WRITE,bh); + } + return 0; +} + +int sync_dev(int dev) +{ + int i; + struct buffer_head * bh; + + bh = start_buffer; + for (i=0 ; ib_dev != dev) + continue; + wait_on_buffer(bh); + if (bh->b_dev == dev && bh->b_dirt) + ll_rw_block(WRITE,bh); + } + sync_inodes(); + bh = start_buffer; + for (i=0 ; ib_dev != dev) + continue; + wait_on_buffer(bh); + if (bh->b_dev == dev && bh->b_dirt) + ll_rw_block(WRITE,bh); + } + return 0; +} + +void inline invalidate_buffers(int dev) +{ + int i; + struct buffer_head * bh; + + bh = start_buffer; + for (i=0 ; ib_dev != dev) + continue; + wait_on_buffer(bh); + if (bh->b_dev == dev) + bh->b_uptodate = bh->b_dirt = 0; + } +} + +/* + * This routine checks whether a floppy has been changed, and + * invalidates all buffer-cache-entries in that case. This + * is a relatively slow routine, so we have to try to minimize using + * it. Thus it is called only upon a 'mount' or 'open'. This + * is the best way of combining speed and utility, I think. + * People changing diskettes in the middle of an operation deserve + * to loose :-) + * + * NOTE! Although currently this is only for floppies, the idea is + * that any additional removable block-device will use this routine, + * and that mount/open needn't know that floppies/whatever are + * special. + */ +void check_disk_change(int dev) +{ + int i; + + if (MAJOR(dev) != 2) + return; + if (!floppy_change(dev & 0x03)) + return; + for (i=0 ; ib_next) + bh->b_next->b_prev = bh->b_prev; + if (bh->b_prev) + bh->b_prev->b_next = bh->b_next; + if (hash(bh->b_dev,bh->b_blocknr) == bh) + hash(bh->b_dev,bh->b_blocknr) = bh->b_next; +/* remove from free list */ + if (!(bh->b_prev_free) || !(bh->b_next_free)) + panic("Free block list corrupted"); + bh->b_prev_free->b_next_free = bh->b_next_free; + bh->b_next_free->b_prev_free = bh->b_prev_free; + if (free_list == bh) + free_list = bh->b_next_free; +} + +static inline void insert_into_queues(struct buffer_head * bh) +{ +/* put at end of free list */ + bh->b_next_free = free_list; + bh->b_prev_free = free_list->b_prev_free; + free_list->b_prev_free->b_next_free = bh; + free_list->b_prev_free = bh; +/* put the buffer in new hash-queue if it has a device */ + bh->b_prev = NULL; + bh->b_next = NULL; + if (!bh->b_dev) + return; + bh->b_next = hash(bh->b_dev,bh->b_blocknr); + hash(bh->b_dev,bh->b_blocknr) = bh; + bh->b_next->b_prev = bh; +} + +static struct buffer_head * find_buffer(int dev, int block) +{ + struct buffer_head * tmp; + + for (tmp = hash(dev,block) ; tmp != NULL ; tmp = tmp->b_next) + if (tmp->b_dev==dev && tmp->b_blocknr==block) + return tmp; + return NULL; +} + +/* + * Why like this, I hear you say... The reason is race-conditions. + * As we don't lock buffers (unless we are readint them, that is), + * something might happen to it while we sleep (ie a read-error + * will force it bad). This shouldn't really happen currently, but + * the code is ready. + */ +struct buffer_head * get_hash_table(int dev, int block) +{ + struct buffer_head * bh; + + for (;;) { + if (!(bh=find_buffer(dev,block))) + return NULL; + bh->b_count++; + wait_on_buffer(bh); + if (bh->b_dev == dev && bh->b_blocknr == block) + return bh; + bh->b_count--; + } +} + +/* + * Ok, this is getblk, and it isn't very clear, again to hinder + * race-conditions. Most of the code is seldom used, (ie repeating), + * so it should be much more efficient than it looks. + * + * The algoritm is changed: hopefully better, and an elusive bug removed. + */ +#define BADNESS(bh) (((bh)->b_dirt<<1)+(bh)->b_lock) +struct buffer_head * getblk(int dev,int block) +{ + struct buffer_head * tmp, * bh; + +repeat: + if (bh = get_hash_table(dev,block)) + return bh; + tmp = free_list; + do { + if (tmp->b_count) + continue; + if (!bh || BADNESS(tmp)b_next_free) != free_list); + if (!bh) { + sleep_on(&buffer_wait); + goto repeat; + } + wait_on_buffer(bh); + if (bh->b_count) + goto repeat; + while (bh->b_dirt) { + sync_dev(bh->b_dev); + wait_on_buffer(bh); + if (bh->b_count) + goto repeat; + } +/* NOTE!! While we slept waiting for this block, somebody else might */ +/* already have added "this" block to the cache. check it */ + if (find_buffer(dev,block)) + goto repeat; +/* OK, FINALLY we know that this buffer is the only one of it's kind, */ +/* and that it's unused (b_count=0), unlocked (b_lock=0), and clean */ + bh->b_count=1; + bh->b_dirt=0; + bh->b_uptodate=0; + remove_from_queues(bh); + bh->b_dev=dev; + bh->b_blocknr=block; + insert_into_queues(bh); + return bh; +} + +void brelse(struct buffer_head * buf) +{ + if (!buf) + return; + wait_on_buffer(buf); + if (!(buf->b_count--)) + panic("Trying to free free buffer"); + wake_up(&buffer_wait); +} + +/* + * bread() reads a specified block and returns the buffer that contains + * it. It returns NULL if the block was unreadable. + */ +struct buffer_head * bread(int dev,int block) +{ + struct buffer_head * bh; + + if (!(bh=getblk(dev,block))) + panic("bread: getblk returned NULL\n"); + if (bh->b_uptodate) + return bh; + ll_rw_block(READ,bh); + wait_on_buffer(bh); + if (bh->b_uptodate) + return bh; + brelse(bh); + return NULL; +} + +#define COPYBLK(from,to) \ +__asm__("cld\n\t" \ + "rep\n\t" \ + "movsl\n\t" \ + ::"c" (BLOCK_SIZE/4),"S" (from),"D" (to) \ + ) + +/* + * bread_page reads four buffers into memory at the desired address. It's + * a function of its own, as there is some speed to be got by reading them + * all at the same time, not waiting for one to be read, and then another + * etc. + */ +void bread_page(unsigned long address,int dev,int b[4]) +{ + struct buffer_head * bh[4]; + int i; + + for (i=0 ; i<4 ; i++) + if (b[i]) { + if (bh[i] = getblk(dev,b[i])) + if (!bh[i]->b_uptodate) + ll_rw_block(READ,bh[i]); + } else + bh[i] = NULL; + for (i=0 ; i<4 ; i++,address += BLOCK_SIZE) + if (bh[i]) { + wait_on_buffer(bh[i]); + if (bh[i]->b_uptodate) + COPYBLK((unsigned long) bh[i]->b_data,address); + brelse(bh[i]); + } +} + +/* + * Ok, breada can be used as bread, but additionally to mark other + * blocks for reading as well. End the argument list with a negative + * number. + */ +struct buffer_head * breada(int dev,int first, ...) +{ + va_list args; + struct buffer_head * bh, *tmp; + + va_start(args,first); + if (!(bh=getblk(dev,first))) + panic("bread: getblk returned NULL\n"); + if (!bh->b_uptodate) + ll_rw_block(READ,bh); + while ((first=va_arg(args,int))>=0) { + tmp=getblk(dev,first); + if (tmp) { + if (!tmp->b_uptodate) + ll_rw_block(READA,bh); + tmp->b_count--; + } + } + va_end(args); + wait_on_buffer(bh); + if (bh->b_uptodate) + return bh; + brelse(bh); + return (NULL); +} + +void buffer_init(long buffer_end) +{ + struct buffer_head * h = start_buffer; + void * b; + int i; + + if (buffer_end == 1<<20) + b = (void *) (640*1024); + else + b = (void *) buffer_end; + while ( (b -= BLOCK_SIZE) >= ((void *) (h+1)) ) { + h->b_dev = 0; + h->b_dirt = 0; + h->b_count = 0; + h->b_lock = 0; + h->b_uptodate = 0; + h->b_wait = NULL; + h->b_next = NULL; + h->b_prev = NULL; + h->b_data = (char *) b; + h->b_prev_free = h-1; + h->b_next_free = h+1; + h++; + NR_BUFFERS++; + if (b == (void *) 0x100000) + b = (void *) 0xA0000; + } + h--; + free_list = start_buffer; + free_list->b_prev_free = h; + h->b_next_free = free_list; + for (i=0;ifilp[fd]; + inode = file->f_inode; + bh = bread(inode->i_dev, inode->i_zone[0]); + dsize = sizeof(struct dir_entry); + ldsize = sizeof(struct linux_dirent); + for (j = 0; j < inode->i_size; j += dsize) + { + if (num + ldsize >= count) + return 0; + + dir = (struct dir_entry*)(bh->b_data + j); + if (dir->inode) + { + mydir.d_ino = dir->inode; + for (i = 0; i < NAME_LEN; i++) + mydir.d_name[i] = dir->name[i]; + mydir.d_off = 0; + mydir.d_reclen = sizeof(mydir); + buf = &mydir; + for (i = 0; i < mydir.d_reclen; i++) + { + put_fs_byte(*(buf + i), ((char*)dirp) + i + num); + } + num += mydir.d_reclen; + } + else + continue; + } + return num; +} \ No newline at end of file