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/*
* fs/direct-io.c
*
* Copyright (C) 2002, Linus Torvalds.
*
* O_DIRECT
*
* 04Jul2002 akpm@zip.com.au
* Initial version
* 11Sep2002 janetinc@us.ibm.com
* added readv/writev support.
* 29Oct2002 akpm@zip.com.au
* rewrote bio_add_page() support.
* 30Oct2002 pbadari@us.ibm.com
* added support for non-aligned IO.
* 06Nov2002 pbadari@us.ibm.com
* added asynchronous IO support.
* 21Jul2003 nathans@sgi.com
* added IO completion notifier.
*/

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/types.h>
#include <linux/fs.h>
#include <linux/mm.h>
#include <linux/slab.h>
#include <linux/highmem.h>
#include <linux/pagemap.h>
#include <linux/bio.h>
#include <linux/wait.h>
#include <linux/err.h>
#include <linux/blkdev.h>
#include <linux/buffer_head.h>
#include <linux/rwsem.h>
#include <linux/uio.h>
#include <asm/atomic.h>

/*
* How many user pages to map in one call to get_user_pages(). This determines
* the size of a structure on the stack.
*/
#define DIO_PAGES 64

/*
* This code generally works in units of "dio_blocks". A dio_block is
* somewhere between the hard sector size and the filesystem block size. it
* is determined on a per-invocation basis. When talking to the filesystem
* we need to convert dio_blocks to fs_blocks by scaling the dio_block quantity
* down by dio->blkfactor. Similarly, fs-blocksize quantities are converted
* to bio_block quantities by shifting left by blkfactor.
*
* If blkfactor is zero then the user's request was aligned to the filesystem's
* blocksize.
*
* lock_type is DIO_LOCKING for regular files on direct-IO-naive filesystems.
* This determines whether we need to do the fancy locking which prevents
* direct-IO from being able to read uninitialised disk blocks. If its zero
* (blockdev) this locking is not done, and if it is DIO_OWN_LOCKING i_mutex is
* not held for the entire direct write (taken briefly, initially, during a
* direct read though, but its never held for the duration of a direct-IO).
*/

struct dio {
/* BIO submission state */
struct bio *bio; /* bio under assembly */
struct inode *inode;
int rw;
loff_t i_size; /* i_size when submitted */
int lock_type; /* doesn't change */
unsigned blkbits; /* doesn't change */
unsigned blkfactor; /* When we're using an alignment which
is finer than the filesystem's soft
blocksize, this specifies how much
finer. blkfactor=2 means 1/4-block
alignment. Does not change */
unsigned start_zero_done; /* flag: sub-blocksize zeroing has
been performed at the start of a
write */
int pages_in_io; /* approximate total IO pages */
size_t size; /* total request size (doesn't change)*/
sector_t block_in_file; /* Current offset into the underlying
file in dio_block units. */
unsigned blocks_available; /* At block_in_file. changes */
sector_t final_block_in_request;/* doesn't change */
unsigned first_block_in_page; /* doesn't change, Used only once */
int boundary; /* prev block is at a boundary */
int reap_counter; /* rate limit reaping */
get_blocks_t *get_blocks; /* block mapping function */
dio_iodone_t *end_io; /* IO completion function */
sector_t final_block_in_bio; /* current final block in bio + 1 */
sector_t next_block_for_io; /* next block to be put under IO,
in dio_blocks units */
struct buffer_head map_bh; /* last get_blocks() result */

/*
* Deferred addition of a page to the dio. These variables are
* private to dio_send_cur_page(), submit_page_section() and
* dio_bio_add_page().
*/
struct page *cur_page; /* The page */
unsigned cur_page_offset; /* Offset into it, in bytes */
unsigned cur_page_len; /* Nr of bytes at cur_page_offset */
sector_t cur_page_block; /* Where it starts */

/*
* Page fetching state. These variables belong to dio_refill_pages().
*/
int curr_page; /* changes */
int total_pages; /* doesn't change */
unsigned long curr_user_address;/* changes */

/*
* Page queue. These variables belong to dio_refill_pages() and
* dio_get_page().
*/
struct page *pages[DIO_PAGES]; /* page buffer */
unsigned head; /* next page to process */
unsigned tail; /* last valid page + 1 */
int page_errors; /* errno from get_user_pages() */

/* BIO completion state */
spinlock_t bio_lock; /* protects BIO fields below */
int bio_count; /* nr bios to be completed */
int bios_in_flight; /* nr bios in flight */
struct bio *bio_list; /* singly linked via bi_private */
struct task_struct *waiter; /* waiting task (NULL if none) */

/* AIO related stuff */
struct kiocb *iocb; /* kiocb */
int is_async; /* is IO async ? */
ssize_t result; /* IO result */
};

/*
* How many pages are in the queue?
*/
static inline unsigned dio_pages_present(struct dio *dio)
{
return dio->tail - dio->head;
}

/*
* Go grab and pin some userspace pages. Typically we'll get 64 at a time.
*/
static int dio_refill_pages(struct dio *dio)
{
int ret;
int nr_pages;

nr_pages = min(dio->total_pages - dio->curr_page, DIO_PAGES);
down_read(&current->mm->mmap_sem);
ret = get_user_pages(
current, /* Task for fault acounting */
current->mm, /* whose pages? */
dio->curr_user_address, /* Where from? */
nr_pages, /* How many pages? */
dio->rw == READ, /* Write to memory? */
0, /* force (?) */
&dio->pages[0],
NULL); /* vmas */
up_read(&current->mm->mmap_sem);

if (ret < 0 && dio->blocks_available && (dio->rw == WRITE)) {
struct page *page = ZERO_PAGE(dio->curr_user_address);
/*
* A memory fault, but the filesystem has some outstanding
* mapped blocks. We need to use those blocks up to avoid
* leaking stale data in the file.
*/
if (dio->page_errors == 0)
dio->page_errors = ret;
page_cache_get(page);
dio->pages[0] = page;
dio->head = 0;
dio->tail = 1;
ret = 0;
goto out;
}

if (ret >= 0) {
dio->curr_user_address += ret * PAGE_SIZE;
dio->curr_page += ret;
dio->head = 0;
dio->tail = ret;
ret = 0;
}
out:
return ret;
}

/*
* Get another userspace page. Returns an ERR_PTR on error. Pages are
* buffered inside the dio so that we can call get_user_pages() against a
* decent number of pages, less frequently. To provide nicer use of the
* L1 cache.
*/
static struct page *dio_get_page(struct dio *dio)
{
if (dio_pages_present(dio) == 0) {
int ret;

ret = dio_refill_pages(dio);
if (ret)
return ERR_PTR(ret);
BUG_ON(dio_pages_present(dio) == 0);
}
return dio->pages[dio->head++];
}

/*
* Called when all DIO BIO I/O has been completed - let the filesystem
* know, if it registered an interest earlier via get_blocks. Pass the
* private field of the map buffer_head so that filesystems can use it
* to hold additional state between get_blocks calls and dio_complete.
*/
static void dio_complete(struct dio *dio, loff_t offset, ssize_t bytes)
{
if (dio->end_io && dio->result)
dio->end_io(dio->iocb, offset, bytes, dio->map_bh.b_private);
if (dio->lock_type == DIO_LOCKING)
up_read(&dio->inode->i_alloc_sem);
}

/*
* Called when a BIO has been processed. If the count goes to zero then IO is
* complete and we can signal this to the AIO layer.
*/
static void finished_one_bio(struct dio *dio)
{
unsigned long flags;

spin_lock_irqsave(&dio->bio_lock, flags);
if (dio->bio_count == 1) {
if (dio->is_async) {
ssize_t transferred;
loff_t offset;

/*
* Last reference to the dio is going away.
* Drop spinlock and complete the DIO.
*/
spin_unlock_irqrestore(&dio->bio_lock, flags);

/* Check for short read case */
transferred = dio->result;
offset = dio->iocb->ki_pos;

if ((dio->rw == READ) &&
((offset + transferred) > dio->i_size))
transferred = dio->i_size - offset;

dio_complete(dio, offset, transferred);

/* Complete AIO later if falling back to buffered i/o */
if (dio->result == dio->size ||
((dio->rw == READ) && dio->result)) {
aio_complete(dio->iocb, transferred, 0);
kfree(dio);
return;
} else {
/*
* Falling back to buffered
*/
spin_lock_irqsave(&dio->bio_lock, flags);
dio->bio_count--;
if (dio->waiter)
wake_up_process(dio->waiter);
spin_unlock_irqrestore(&dio->bio_lock, flags);
return;
}
}
}
dio->bio_count--;
spin_unlock_irqrestore(&dio->bio_lock, flags);
}

static int dio_bio_complete(struct dio *dio, struct bio *bio);
/*
* Asynchronous IO callback.
*/
static int dio_bio_end_aio(struct bio *bio, unsigned int bytes_done, int error)
{
struct dio *dio = bio->bi_private;

if (bio->bi_size)
return 1;

/* cleanup the bio */
dio_bio_complete(dio, bio);
return 0;
}

/*
* The BIO completion handler simply queues the BIO up for the process-context
* handler.
*
* During I/O bi_private points at the dio. After I/O, bi_private is used to
* implement a singly-linked list of completed BIOs, at dio->bio_list.
*/
static int dio_bio_end_io(struct bio *bio, unsigned int bytes_done, int error)
{
struct dio *dio = bio->bi_private;
unsigned long flags;

if (bio->bi_size)
return 1;

spin_lock_irqsave(&dio->bio_lock, flags);
bio->bi_private = dio->bio_list;
dio->bio_list = bio;
dio->bios_in_flight--;
if (dio->waiter && dio->bios_in_flight == 0)
wake_up_process(dio->waiter);
spin_unlock_irqrestore(&dio->bio_lock, flags);
return 0;
}

static int
dio_bio_alloc(struct dio *dio, struct block_device *bdev,
sector_t first_sector, int nr_vecs)
{
struct bio *bio;

bio = bio_alloc(GFP_KERNEL, nr_vecs);
if (bio == NULL)
return -ENOMEM;

bio->bi_bdev = bdev;
bio->bi_sector = first_sector;
if (dio->is_async)
bio->bi_end_io = dio_bio_end_aio;
else
bio->bi_end_io = dio_bio_end_io;

dio->bio = bio;
return 0;
}

/*
* In the AIO read case we speculatively dirty the pages before starting IO.
* During IO completion, any of these pages which happen to have been written
* back will be redirtied by bio_check_pages_dirty().
*/
static void dio_bio_submit(struct dio *dio)
{
struct bio *bio = dio->bio;
unsigned long flags;

bio->bi_private = dio;
spin_lock_irqsave(&dio->bio_lock, flags);
dio->bio_count++;
dio->bios_in_flight++;
spin_unlock_irqrestore(&dio->bio_lock, flags);
if (dio->is_async && dio->rw == READ)
bio_set_pages_dirty(bio);
submit_bio(dio->rw, bio);

dio->bio = NULL;
dio->boundary = 0;
}

/*
* Release any resources in case of a failure
*/
static void dio_cleanup(struct dio *dio)
{
while (dio_pages_present(dio))
page_cache_release(dio_get_page(dio));
}

/*
* Wait for the next BIO to complete. Remove it and return it.
*/
static struct bio *dio_await_one(struct dio *dio)
{
unsigned long flags;
struct bio *bio;

spin_lock_irqsave(&dio->bio_lock, flags);
while (dio->bio_list == NULL) {
set_current_state(TASK_UNINTERRUPTIBLE);
if (dio->bio_list == NULL) {
dio->waiter = current;
spin_unlock_irqrestore(&dio->bio_lock, flags);
blk_run_address_space(dio->inode->i_mapping);
io_schedule();
spin_lock_irqsave(&dio->bio_lock, flags);
dio->waiter = NULL;
}
set_current_state(TASK_RUNNING);
}
bio = dio->bio_list;
dio->bio_list = bio->bi_private;
spin_unlock_irqrestore(&dio->bio_lock, flags);
return bio;
}

/*
* Process one completed BIO. No locks are held.
*/
static int dio_bio_complete(struct dio *dio, struct bio *bio)
{
const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
struct bio_vec *bvec = bio->bi_io_vec;
int page_no;

if (!uptodate)
dio->result = -EIO;

if (dio->is_async && dio->rw == READ) {
bio_check_pages_dirty(bio); /* transfers ownership */
} else {
for (page_no = 0; page_no < bio->bi_vcnt; page_no++) {
struct page *page = bvec[page_no].bv_page;

if (dio->rw == READ && !PageCompound(page))
set_page_dirty_lock(page);
page_cache_release(page);
}
bio_put(bio);
}
finished_one_bio(dio);
return uptodate ? 0 : -EIO;
}

/*
* Wait on and process all in-flight BIOs.
*/
static int dio_await_completion(struct dio *dio)
{
int ret = 0;

if (dio->bio)
dio_bio_submit(dio);

/*
* The bio_lock is not held for the read of bio_count.
* This is ok since it is the dio_bio_complete() that changes
* bio_count.
*/
while (dio->bio_count) {
struct bio *bio = dio_await_one(dio);
int ret2;

ret2 = dio_bio_complete(dio, bio);
if (ret == 0)
ret = ret2;
}
return ret;
}

/*
* A really large O_DIRECT read or write can generate a lot of BIOs. So
* to keep the memory consumption sane we periodically reap any completed BIOs
* during the BIO generation phase.
*
* This also helps to limit the peak amount of pinned userspace memory.
*/
static int dio_bio_reap(struct dio *dio)
{
int ret = 0;

if (dio->reap_counter++ >= 64) {
while (dio->bio_list) {
unsigned long flags;
struct bio *bio;
int ret2;

spin_lock_irqsave(&dio->bio_lock, flags);
bio = dio->bio_list;
dio->bio_list = bio->bi_private;
spin_unlock_irqrestore(&dio->bio_lock, flags);
ret2 = dio_bio_complete(dio, bio);
if (ret == 0)
ret = ret2;
}
dio->reap_counter = 0;
}
return ret;
}

/*
* Call into the fs to map some more disk blocks. We record the current number
* of available blocks at dio->blocks_available. These are in units of the
* fs blocksize, (1 << inode->i_blkbits).
*
* The fs is allowed to map lots of blocks at once. If it wants to do that,
* it uses the passed inode-relative block number as the file offset, as usual.
*
* get_blocks() is passed the number of i_blkbits-sized blocks which direct_io
* has remaining to do. The fs should not map more than this number of blocks.
*
* If the fs has mapped a lot of blocks, it should populate bh->b_size to
* indicate how much contiguous disk space has been made available at
* bh->b_blocknr.
*
* If *any* of the mapped blocks are new, then the fs must set buffer_new().
* This isn't very efficient...
*
* In the case of filesystem holes: the fs may return an arbitrarily-large
* hole by returning an appropriate value in b_size and by clearing
* buffer_mapped(). However the direct-io code will only process holes one
* block at a time - it will repeatedly call get_blocks() as it walks the hole.
*/
static int get_more_blocks(struct dio *dio)
{
int ret;
struct buffer_head *map_bh = &dio->map_bh;
sector_t fs_startblk; /* Into file, in filesystem-sized blocks */
unsigned long fs_count; /* Number of filesystem-sized blocks */
unsigned long dio_count;/* Number of dio_block-sized blocks */
unsigned long blkmask;
int create;

/*
* If there was a memory error and we've overwritten all the
* mapped blocks then we can now return that memory error
*/
ret = dio->page_errors;
if (ret == 0) {
map_bh->b_state = 0;
map_bh->b_size = 0;
BUG_ON(dio->block_in_file >= dio->final_block_in_request);
fs_startblk = dio->block_in_file >> dio->blkfactor;
dio_count = dio->final_block_in_request - dio->block_in_file;
fs_count = dio_count >> dio->blkfactor;
blkmask = (1 << dio->blkfactor) - 1;
if (dio_count & blkmask)
fs_count++;

create = dio->rw == WRITE;
if (dio->lock_type == DIO_LOCKING) {
if (dio->block_in_file < (i_size_read(dio->inode) >>
dio->blkbits))
create = 0;
} else if (dio->lock_type == DIO_NO_LOCKING) {
create = 0;
}
/*
* For writes inside i_size we forbid block creations: only
* overwrites are permitted. We fall back to buffered writes
* at a higher level for inside-i_size block-instantiating
* writes.
*/
ret = (*dio->get_blocks)(dio->inode, fs_startblk, fs_count,
map_bh, create);
}
return ret;
}

/*
* There is no bio. Make one now.
*/
static int dio_new_bio(struct dio *dio, sector_t start_sector)
{
sector_t sector;
int ret, nr_pages;

ret = dio_bio_reap(dio);
if (ret)
goto out;
sector = start_sector << (dio->blkbits - 9);
nr_pages = min(dio->pages_in_io, bio_get_nr_vecs(dio->map_bh.b_bdev));
BUG_ON(nr_pages <= 0);
ret = dio_bio_alloc(dio, dio->map_bh.b_bdev, sector, nr_pages);
dio->boundary = 0;
out:
return ret;
}

/*
* Attempt to put the current chunk of 'cur_page' into the current BIO. If
* that was successful then update final_block_in_bio and take a ref against
* the just-added page.
*
* Return zero on success. Non-zero means the caller needs to start a new BIO.
*/
static int dio_bio_add_page(struct dio *dio)
{
int ret;

ret = bio_add_page(dio->bio, dio->cur_page,
dio->cur_page_len, dio->cur_page_offset);
if (ret == dio->cur_page_len) {
/*
* Decrement count only, if we are done with this page
*/
if ((dio->cur_page_len + dio->cur_page_offset) == PAGE_SIZE)
dio->pages_in_io--;
page_cache_get(dio->cur_page);
dio->final_block_in_bio = dio->cur_page_block +
(dio->cur_page_len >> dio->blkbits);
ret = 0;
} else {
ret = 1;
}
return ret;
}

/*
* Put cur_page under IO. The section of cur_page which is described by
* cur_page_offset,cur_page_len is put into a BIO. The section of cur_page
* starts on-disk at cur_page_block.
*
* We take a ref against the page here (on behalf of its presence in the bio).
*
* The caller of this function is responsible for removing cur_page from the
* dio, and for dropping the refcount which came from that presence.
*/
static int dio_send_cur_page(struct dio *dio)
{
int ret = 0;

if (dio->bio) {
/*
* See whether this new request is contiguous with the old
*/
if (dio->final_block_in_bio != dio->cur_page_block)
dio_bio_submit(dio);
/*
* Submit now if the underlying fs is about to perform a
* metadata read
*/
if (dio->boundary)
dio_bio_submit(dio);
}

if (dio->bio == NULL) {
ret = dio_new_bio(dio, dio->cur_page_block);
if (ret)
goto out;
}

if (dio_bio_add_page(dio) != 0) {
dio_bio_submit(dio);
ret = dio_new_bio(dio, dio->cur_page_block);
if (ret == 0) {
ret = dio_bio_add_page(dio);
BUG_ON(ret != 0);
}
}
out:
return ret;
}

/*
* An autonomous function to put a chunk of a page under deferred IO.
*
* The caller doesn't actually know (or care) whether this piece of page is in
* a BIO, or is under IO or whatever. We just take care of all possible
* situations here. The separation between the logic of do_direct_IO() and
* that of submit_page_section() is important for clarity. Please don't break.
*
* The chunk of page starts on-disk at blocknr.
*
* We perform deferred IO, by recording the last-submitted page inside our
* private part of the dio structure. If possible, we just expand the IO
* across that page here.
*
* If that doesn't work out then we put the old page into the bio and add this
* page to the dio instead.
*/
static int
submit_page_section(struct dio *dio, struct page *page,
unsigned offset, unsigned len, sector_t blocknr)
{
int ret = 0;

/*
* Can we just grow the current page's presence in the dio?
*/
if ( (dio->cur_page == page) &&
(dio->cur_page_offset + dio->cur_page_len == offset) &&
(dio->cur_page_block +
(dio->cur_page_len >> dio->blkbits) == blocknr)) {
dio->cur_page_len += len;

/*
* If dio->boundary then we want to schedule the IO now to
* avoid metadata seeks.
*/
if (dio->boundary) {
ret = dio_send_cur_page(dio);
page_cache_release(dio->cur_page);
dio->cur_page = NULL;
}
goto out;
}

/*
* If there's a deferred page already there then send it.
*/
if (dio->cur_page) {
ret = dio_send_cur_page(dio);
page_cache_release(dio->cur_page);
dio->cur_page = NULL;
if (ret)
goto out;
}

page_cache_get(page); /* It is in dio */
dio->cur_page = page;
dio->cur_page_offset = offset;
dio->cur_page_len = len;
dio->cur_page_block = blocknr;
out:
return ret;
}

/*
* Clean any dirty buffers in the blockdev mapping which alias newly-created
* file blocks. Only called for S_ISREG files - blockdevs do not set
* buffer_new
*/
static void clean_blockdev_aliases(struct dio *dio)
{
unsigned i;
unsigned nblocks;

nblocks = dio->map_bh.b_size >> dio->inode->i_blkbits;

for (i = 0; i < nblocks; i++) {
unmap_underlying_metadata(dio->map_bh.b_bdev,
dio->map_bh.b_blocknr + i);
}
}

/*
* If we are not writing the entire block and get_block() allocated
* the block for us, we need to fill-in the unused portion of the
* block with zeros. This happens only if user-buffer, fileoffset or
* io length is not filesystem block-size multiple.
*
* `end' is zero if we're doing the start of the IO, 1 at the end of the
* IO.
*/
static void dio_zero_block(struct dio *dio, int end)
{
unsigned dio_blocks_per_fs_block;
unsigned this_chunk_blocks; /* In dio_blocks */
unsigned this_chunk_bytes;
struct page *page;

dio->start_zero_done = 1;
if (!dio->blkfactor || !buffer_new(&dio->map_bh))
return;

dio_blocks_per_fs_block = 1 << dio->blkfactor;
this_chunk_blocks = dio->block_in_file & (dio_blocks_per_fs_block - 1);

if (!this_chunk_blocks)
return;

/*
* We need to zero out part of an fs block. It is either at the
* beginning or the end of the fs block.
*/
if (end)
this_chunk_blocks = dio_blocks_per_fs_block - this_chunk_blocks;

this_chunk_bytes = this_chunk_blocks << dio->blkbits;

page = ZERO_PAGE(dio->curr_user_address);
if (submit_page_section(dio, page, 0, this_chunk_bytes,
dio->next_block_for_io))
return;

dio->next_block_for_io += this_chunk_blocks;
}

/*
* Walk the user pages, and the file, mapping blocks to disk and generating
* a sequence of (page,offset,len,block) mappings. These mappings are injected
* into submit_page_section(), which takes care of the next stage of submission
*
* Direct IO against a blockdev is different from a file. Because we can
* happily perform page-sized but 512-byte aligned IOs. It is important that
* blockdev IO be able to have fine alignment and large sizes.
*
* So what we do is to permit the ->get_blocks function to populate bh.b_size
* with the size of IO which is permitted at this offset and this i_blkbits.
*
* For best results, the blockdev should be set up with 512-byte i_blkbits and
* it should set b_size to PAGE_SIZE or more inside get_blocks(). This gives
* fine alignment but still allows this function to work in PAGE_SIZE units.
*/
static int do_direct_IO(struct dio *dio)
{
const unsigned blkbits = dio->blkbits;
const unsigned blocks_per_page = PAGE_SIZE >> blkbits;
struct page *page;
unsigned block_in_page;
struct buffer_head *map_bh = &dio->map_bh;
int ret = 0;

/* The I/O can start at any block offset within the first page */
block_in_page = dio->first_block_in_page;

while (dio->block_in_file < dio->final_block_in_request) {
page = dio_get_page(dio);
if (IS_ERR(page)) {
ret = PTR_ERR(page);
goto out;
}

while (block_in_page < blocks_per_page) {
unsigned offset_in_page = block_in_page << blkbits;
unsigned this_chunk_bytes; /* # of bytes mapped */
unsigned this_chunk_blocks; /* # of blocks */
unsigned u;

if (dio->blocks_available == 0) {
/*
* Need to go and map some more disk
*/
unsigned long blkmask;
unsigned long dio_remainder;

ret = get_more_blocks(dio);
if (ret) {
page_cache_release(page);
goto out;
}
if (!buffer_mapped(map_bh))
goto do_holes;

dio->blocks_available =
map_bh->b_size >> dio->blkbits;
dio->next_block_for_io =
map_bh->b_blocknr << dio->blkfactor;
if (buffer_new(map_bh))
clean_blockdev_aliases(dio);

if (!dio->blkfactor)
goto do_holes;

blkmask = (1 << dio->blkfactor) - 1;
dio_remainder = (dio->block_in_file & blkmask);

/*
* If we are at the start of IO and that IO
* starts partway into a fs-block,
* dio_remainder will be non-zero. If the IO
* is a read then we can simply advance the IO
* cursor to the first block which is to be
* read. But if the IO is a write and the
* block was newly allocated we cannot do that;
* the start of the fs block must be zeroed out
* on-disk
*/
if (!buffer_new(map_bh))
dio->next_block_for_io += dio_remainder;
dio->blocks_available -= dio_remainder;
}
do_holes:
/* Handle holes */
if (!buffer_mapped(map_bh)) {
char *kaddr;
loff_t i_size_aligned;

/* AKPM: eargh, -ENOTBLK is a hack */
if (dio->rw == WRITE) {
page_cache_release(page);
return -ENOTBLK;
}

/*
* Be sure to account for a partial block as the
* last block in the file
*/
i_size_aligned = ALIGN(i_size_read(dio->inode),
1 << blkbits);
if (dio->block_in_file >=
i_size_aligned >> blkbits) {
/* We hit eof */
page_cache_release(page);
goto out;
}
kaddr = kmap_atomic(page, KM_USER0);
memset(kaddr + (block_in_page << blkbits),
0, 1 << blkbits);
flush_dcache_page(page);
kunmap_atomic(kaddr, KM_USER0);
dio->block_in_file++;
block_in_page++;
goto next_block;
}

/*
* If we're performing IO which has an alignment which
* is finer than the underlying fs, go check to see if
* we must zero out the start of this block.
*/
if (unlikely(dio->blkfactor && !dio->start_zero_done))
dio_zero_block(dio, 0);

/*
* Work out, in this_chunk_blocks, how much disk we
* can add to this page
*/
this_chunk_blocks = dio->blocks_available;
u = (PAGE_SIZE - offset_in_page) >> blkbits;
if (this_chunk_blocks > u)
this_chunk_blocks = u;
u = dio->final_block_in_request - dio->block_in_file;
if (this_chunk_blocks > u)
this_chunk_blocks = u;
this_chunk_bytes = this_chunk_blocks << blkbits;
BUG_ON(this_chunk_bytes == 0);

dio->boundary = buffer_boundary(map_bh);
ret = submit_page_section(dio, page, offset_in_page,
this_chunk_bytes, dio->next_block_for_io);
if (ret) {
page_cache_release(page);
goto out;
}
dio->next_block_for_io += this_chunk_blocks;

dio->block_in_file += this_chunk_blocks;
block_in_page += this_chunk_blocks;
dio->blocks_available -= this_chunk_blocks;
next_block:
if (dio->block_in_file > dio->final_block_in_request)
BUG();
if (dio->block_in_file == dio->final_block_in_request)
break;
}

/* Drop the ref which was taken in get_user_pages() */
page_cache_release(page);
block_in_page = 0;
}
out:
return ret;
}

/*
* Releases both i_mutex and i_alloc_sem
*/
static ssize_t
direct_io_worker(int rw, struct kiocb *iocb, struct inode *inode,
const struct iovec *iov, loff_t offset, unsigned long nr_segs,
unsigned blkbits, get_blocks_t get_blocks, dio_iodone_t end_io,
struct dio *dio)
{
unsigned long user_addr;
int seg;
ssize_t ret = 0;
ssize_t ret2;
size_t bytes;

dio->bio = NULL;
dio->inode = inode;
dio->rw = rw;
dio->blkbits = blkbits;
dio->blkfactor = inode->i_blkbits - blkbits;
dio->start_zero_done = 0;
dio->size = 0;
dio->block_in_file = offset >> blkbits;
dio->blocks_available = 0;
dio->cur_page = NULL;

dio->boundary = 0;
dio->reap_counter = 0;
dio->get_blocks = get_blocks;
dio->end_io = end_io;
dio->map_bh.b_private = NULL;
dio->final_block_in_bio = -1;
dio->next_block_for_io = -1;

dio->page_errors = 0;
dio->result = 0;
dio->iocb = iocb;
dio->i_size = i_size_read(inode);

/*
* BIO completion state.
*
* ->bio_count starts out at one, and we decrement it to zero after all
* BIOs are submitted. This to avoid the situation where a really fast
* (or synchronous) device could take the count to zero while we're
* still submitting BIOs.
*/
dio->bio_count = 1;
dio->bios_in_flight = 0;
spin_lock_init(&dio->bio_lock);
dio->bio_list = NULL;
dio->waiter = NULL;

/*
* In case of non-aligned buffers, we may need 2 more
* pages since we need to zero out first and last block.
*/
if (unlikely(dio->blkfactor))
dio->pages_in_io = 2;
else
dio->pages_in_io = 0;

for (seg = 0; seg < nr_segs; seg++) {
user_addr = (unsigned long)iov[seg].iov_base;
dio->pages_in_io +=
((user_addr+iov[seg].iov_len +PAGE_SIZE-1)/PAGE_SIZE
- user_addr/PAGE_SIZE);
}

for (seg = 0; seg < nr_segs; seg++) {
user_addr = (unsigned long)iov[seg].iov_base;
dio->size += bytes = iov[seg].iov_len;

/* Index into the first page of the first block */
dio->first_block_in_page = (user_addr & ~PAGE_MASK) >> blkbits;
dio->final_block_in_request = dio->block_in_file +
(bytes >> blkbits);
/* Page fetching state */
dio->head = 0;
dio->tail = 0;
dio->curr_page = 0;

dio->total_pages = 0;
if (user_addr & (PAGE_SIZE-1)) {
dio->total_pages++;
bytes -= PAGE_SIZE - (user_addr & (PAGE_SIZE - 1));
}
dio->total_pages += (bytes + PAGE_SIZE - 1) / PAGE_SIZE;
dio->curr_user_address = user_addr;

ret = do_direct_IO(dio);

dio->result += iov[seg].iov_len -
((dio->final_block_in_request - dio->block_in_file) <<
blkbits);

if (ret) {
dio_cleanup(dio);
break;
}
} /* end iovec loop */

if (ret == -ENOTBLK && rw == WRITE) {
/*
* The remaining part of the request will be
* be handled by buffered I/O when we return
*/
ret = 0;
}
/*
* There may be some unwritten disk at the end of a part-written
* fs-block-sized block. Go zero that now.
*/
dio_zero_block(dio, 1);

if (dio->cur_page) {
ret2 = dio_send_cur_page(dio);
if (ret == 0)
ret = ret2;
page_cache_release(dio->cur_page);
dio->cur_page = NULL;
}
if (dio->bio)
dio_bio_submit(dio);

/*
* It is possible that, we return short IO due to end of file.
* In that case, we need to release all the pages we got hold on.
*/
dio_cleanup(dio);

/*
* All block lookups have been performed. For READ requests
* we can let i_mutex go now that its achieved its purpose
* of protecting us from looking up uninitialized blocks.
*/
if ((rw == READ) && (dio->lock_type == DIO_LOCKING))
mutex_unlock(&dio->inode->i_mutex);

/*
* OK, all BIOs are submitted, so we can decrement bio_count to truly
* reflect the number of to-be-processed BIOs.
*/
if (dio->is_async) {
int should_wait = 0;

if (dio->result < dio->size && rw == WRITE) {
dio->waiter = current;
should_wait = 1;
}
if (ret == 0)
ret = dio->result;
finished_one_bio(dio); /* This can free the dio */
blk_run_address_space(inode->i_mapping);
if (should_wait) {
unsigned long flags;
/*
* Wait for already issued I/O to drain out and
* release its references to user-space pages
* before returning to fallback on buffered I/O
*/

spin_lock_irqsave(&dio->bio_lock, flags);
set_current_state(TASK_UNINTERRUPTIBLE);
while (dio->bio_count) {
spin_unlock_irqrestore(&dio->bio_lock, flags);
io_schedule();
spin_lock_irqsave(&dio->bio_lock, flags);
set_current_state(TASK_UNINTERRUPTIBLE);
}
spin_unlock_irqrestore(&dio->bio_lock, flags);
set_current_state(TASK_RUNNING);
kfree(dio);
}
} else {
ssize_t transferred = 0;

finished_one_bio(dio);
ret2 = dio_await_completion(dio);
if (ret == 0)
ret = ret2;
if (ret == 0)
ret = dio->page_errors;
if (dio->result) {
loff_t i_size = i_size_read(inode);

transferred = dio->result;
/*
* Adjust the return value if the read crossed a
* non-block-aligned EOF.
*/
if (rw == READ && (offset + transferred > i_size))
transferred = i_size - offset;
}
dio_complete(dio, offset, transferred);
if (ret == 0)
ret = transferred;

/* We could have also come here on an AIO file extend */
if (!is_sync_kiocb(iocb) && rw == WRITE &&
ret >= 0 && dio->result == dio->size)
/*
* For AIO writes where we have completed the
* i/o, we have to mark the the aio complete.
*/
aio_complete(iocb, ret, 0);
kfree(dio);
}
return ret;
}

/*
* This is a library function for use by filesystem drivers.
* The locking rules are governed by the dio_lock_type parameter.
*
* DIO_NO_LOCKING (no locking, for raw block device access)
* For writes, i_mutex is not held on entry; it is never taken.
*
* DIO_LOCKING (simple locking for regular files)
* For writes we are called under i_mutex and return with i_mutex held, even though
* it is internally dropped.
* For reads, i_mutex is not held on entry, but it is taken and dropped before
* returning.
*
* DIO_OWN_LOCKING (filesystem provides synchronisation and handling of
* uninitialised data, allowing parallel direct readers and writers)
* For writes we are called without i_mutex, return without it, never touch it.
* For reads, i_mutex is held on entry and will be released before returning.
*
* Additional i_alloc_sem locking requirements described inline below.
*/
ssize_t
__blockdev_direct_IO(int rw, struct kiocb *iocb, struct inode *inode,
struct block_device *bdev, const struct iovec *iov, loff_t offset,
unsigned long nr_segs, get_blocks_t get_blocks, dio_iodone_t end_io,
int dio_lock_type)
{
int seg;
size_t size;
unsigned long addr;
unsigned blkbits = inode->i_blkbits;
unsigned bdev_blkbits = 0;
unsigned blocksize_mask = (1 << blkbits) - 1;
ssize_t retval = -EINVAL;
loff_t end = offset;
struct dio *dio;
int reader_with_isem = (rw == READ && dio_lock_type == DIO_OWN_LOCKING);

if (rw & WRITE)
current->flags |= PF_SYNCWRITE;

if (bdev)
bdev_blkbits = blksize_bits(bdev_hardsect_size(bdev));

if (offset & blocksize_mask) {
if (bdev)
blkbits = bdev_blkbits;
blocksize_mask = (1 << blkbits) - 1;
if (offset & blocksize_mask)
goto out;
}

/* Check the memory alignment. Blocks cannot straddle pages */
for (seg = 0; seg < nr_segs; seg++) {
addr = (unsigned long)iov[seg].iov_base;
size = iov[seg].iov_len;
end += size;
if ((addr & blocksize_mask) || (size & blocksize_mask)) {
if (bdev)
blkbits = bdev_blkbits;
blocksize_mask = (1 << blkbits) - 1;
if ((addr & blocksize_mask) || (size & blocksize_mask))
goto out;
}
}

dio = kmalloc(sizeof(*dio), GFP_KERNEL);
retval = -ENOMEM;
if (!dio)
goto out;

/*
* For block device access DIO_NO_LOCKING is used,
* neither readers nor writers do any locking at all
* For regular files using DIO_LOCKING,
* readers need to grab i_mutex and i_alloc_sem
* writers need to grab i_alloc_sem only (i_mutex is already held)
* For regular files using DIO_OWN_LOCKING,
* neither readers nor writers take any locks here
* (i_mutex is already held and release for writers here)
*/
dio->lock_type = dio_lock_type;
if (dio_lock_type != DIO_NO_LOCKING) {
/* watch out for a 0 len io from a tricksy fs */
if (rw == READ && end > offset) {
struct address_space *mapping;

mapping = iocb->ki_filp->f_mapping;
if (dio_lock_type != DIO_OWN_LOCKING) {
mutex_lock(&inode->i_mutex);
reader_with_isem = 1;
}

retval = filemap_write_and_wait_range(mapping, offset,
end - 1);
if (retval) {
kfree(dio);
goto out;
}

if (dio_lock_type == DIO_OWN_LOCKING) {
mutex_unlock(&inode->i_mutex);
reader_with_isem = 0;
}
}

if (dio_lock_type == DIO_LOCKING)
down_read(&inode->i_alloc_sem);
}

/*
* For file extending writes updating i_size before data
* writeouts complete can expose uninitialized blocks. So
* even for AIO, we need to wait for i/o to complete before
* returning in this case.
*/
dio->is_async = !is_sync_kiocb(iocb) && !((rw == WRITE) &&
(end > i_size_read(inode)));

retval = direct_io_worker(rw, iocb, inode, iov, offset,
nr_segs, blkbits, get_blocks, end_io, dio);

if (rw == READ && dio_lock_type == DIO_LOCKING)
reader_with_isem = 0;

out:
if (reader_with_isem)
mutex_unlock(&inode->i_mutex);
if (rw & WRITE)
current->flags &= ~PF_SYNCWRITE;
return retval;
}
EXPORT_SYMBOL(__blockdev_direct_IO);
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