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fuse: fix alignment in short read optimization for async_dio 

The bug was introduced with async_dio feature: trying to optimize short reads,
we cut number-of-bytes-to-read to i_size boundary. Hence the following example:

	truncate --size=300 /mnt/file
	dd if=/mnt/file of=/dev/null iflag=direct

led to FUSE_READ request of 300 bytes size. This turned out to be problem
for userspace fuse implementations who rely on assumption that kernel fuse
does not change alignment of request from client FS.

The patch turns off the optimization if async_dio is disabled. And, if it's
enabled, the patch fixes adjustment of number-of-bytes-to-read to preserve
alignment.

Note, that we cannot throw out short read optimization entirely because
otherwise a direct read of a huge size issued on a tiny file would generate
a huge amount of fuse requests and most of them would be ACKed by userspace
with zero bytes read.

Signed-off-by: Maxim Patlasov <MPatlasov@parallels.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
This commit is contained in:
Maxim Patlasov 2013-05-30 16:41:34 +04:00 committed by Miklos Szeredi
parent c9ecf989cc
commit e5c5f05dca
1 changed files with 10 additions and 4 deletions
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14
fs/fuse/file.c
View File

@ -2373,6 +2373,11 @@ static void fuse_do_truncate(struct file *file)
fuse_do_setattr(inode, &attr, file); fuse_do_setattr(inode, &attr, file);
} }
static inline loff_t fuse_round_up(loff_t off)
{
return round_up(off, FUSE_MAX_PAGES_PER_REQ << PAGE_SHIFT);
}
static ssize_t static ssize_t
fuse_direct_IO(int rw, struct kiocb *iocb, const struct iovec *iov, fuse_direct_IO(int rw, struct kiocb *iocb, const struct iovec *iov,
loff_t offset, unsigned long nr_segs) loff_t offset, unsigned long nr_segs)
@ -2380,6 +2385,7 @@ fuse_direct_IO(int rw, struct kiocb *iocb, const struct iovec *iov,
ssize_t ret = 0; ssize_t ret = 0;
struct file *file = iocb->ki_filp; struct file *file = iocb->ki_filp;
struct fuse_file *ff = file->private_data; struct fuse_file *ff = file->private_data;
bool async_dio = ff->fc->async_dio;
loff_t pos = 0; loff_t pos = 0;
struct inode *inode; struct inode *inode;
loff_t i_size; loff_t i_size;
@ -2391,10 +2397,10 @@ fuse_direct_IO(int rw, struct kiocb *iocb, const struct iovec *iov,
i_size = i_size_read(inode); i_size = i_size_read(inode);
/* optimization for short read */ /* optimization for short read */
if (rw != WRITE && offset + count > i_size) { if (async_dio && rw != WRITE && offset + count > i_size) {
if (offset >= i_size) if (offset >= i_size)
return 0; return 0;
count = i_size - offset; count = min_t(loff_t, count, fuse_round_up(i_size - offset));
} }
io = kmalloc(sizeof(struct fuse_io_priv), GFP_KERNEL); io = kmalloc(sizeof(struct fuse_io_priv), GFP_KERNEL);
@ -2412,7 +2418,7 @@ fuse_direct_IO(int rw, struct kiocb *iocb, const struct iovec *iov,
* By default, we want to optimize all I/Os with async request * By default, we want to optimize all I/Os with async request
* submission to the client filesystem if supported. * submission to the client filesystem if supported.
*/ */
io->async = ff->fc->async_dio; io->async = async_dio;
io->iocb = iocb; io->iocb = iocb;
/* /*
@ -2420,7 +2426,7 @@ fuse_direct_IO(int rw, struct kiocb *iocb, const struct iovec *iov,
* to wait on real async I/O requests, so we must submit this request * to wait on real async I/O requests, so we must submit this request
* synchronously. * synchronously.
*/ */
if (!is_sync_kiocb(iocb) && (offset + count > i_size)) if (!is_sync_kiocb(iocb) && (offset + count > i_size) && rw == WRITE)
io->async = false; io->async = false;
if (rw == WRITE) if (rw == WRITE)