android_kernel_xiaomi_sm8350/fs/direct-io.c
Chen, Kenneth W 174e27c607 [PATCH] direct-io: bug fix in dio handling write error
There is a bug in direct-io on propagating write error up to the higher I/O
layer.  When performing an async ODIRECT write to a block device, if a
device error occurred (like media error or disk is pulled), the error code
is only propagated from device driver to the DIO layer.  The error code
stops at finished_one_bio().  The aysnc write, however, is supposedly have
a corresponding AIO event with appropriate return code (in this case -EIO).
 Application which waits on the async write event, will hang forever since
such AIO event is lost forever (if such app did not use the timeout option
in io_getevents call.  Regardless, an AIO event is lost).

The discovery of above bug leads to another discovery of potential race
window with dio->result.  The fundamental problem is that dio->result is
overloaded with dual use: an indicator of fall back path for partial dio
write, and an error indicator used in the I/O completion path.  In the
event of device error, the setting of -EIO to dio->result clashes with
value used to track partial write that activates the fall back path.

It was also pointed out that it is impossible to use dio->result to track
partial write and at the same time to track error returned from device
driver.  Because direct_io_work can only determines whether it is a partial
write at the end of io submission and in mid stream of those io submission,
a return code could be coming back from the driver.  Thus messing up all
the subsequent logic.

Proposed fix is to separating out error code returned by the IO completion
path from partial IO submit tracking.  A new variable is added to dio
structure specifically to track io error returned in the completion path.

Signed-off-by: Ken Chen <kenneth.w.chen@intel.com>
Acked-by: Zach Brown <zach.brown@oracle.com>
Acked-by: Suparna Bhattacharya <suparna@in.ibm.com>
Cc: Badari Pulavarty <pbadari@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-03-25 08:23:00 -08:00

1291 lines
35 KiB
C

/*
* 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 ? */
int io_error; /* IO error in completion path */
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;
/* check for error in completion path */
if (dio->io_error)
transferred = dio->io_error;
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->io_error = -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->io_error = 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 we are called under i_mutex and return with i_mutex held, even
* though it may be internally dropped.
*
* 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 release_i_mutex = 0;
int acquire_i_mutex = 0;
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
*/
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);
release_i_mutex = 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);
acquire_i_mutex = 1;
}
}
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)
release_i_mutex = 0;
out:
if (release_i_mutex)
mutex_unlock(&inode->i_mutex);
else if (acquire_i_mutex)
mutex_lock(&inode->i_mutex);
if (rw & WRITE)
current->flags &= ~PF_SYNCWRITE;
return retval;
}
EXPORT_SYMBOL(__blockdev_direct_IO);