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authorMaxim Patlasov <mpatlasov@parallels.com>2013-05-30 16:41:34 +0400
committerMiklos Szeredi <mszeredi@suse.cz>2013-06-03 15:15:42 +0200
commite5c5f05dca0cf90f0f3bb1aea85dcf658baff185 (patch)
treed6290697847d61da2c4a183d9ea521989a814a43
parentc9ecf989cc7626e9edf8abef79f64b909542129b (diff)
downloadvexpress-lsk-e5c5f05dca0cf90f0f3bb1aea85dcf658baff185.tar.gz
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>
-rw-r--r--fs/fuse/file.c14
1 files changed, 10 insertions, 4 deletions
diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index b3ad8d61a16..e570081f9f7 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -2373,6 +2373,11 @@ static void fuse_do_truncate(struct file *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
fuse_direct_IO(int rw, struct kiocb *iocb, const struct iovec *iov,
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;
struct file *file = iocb->ki_filp;
struct fuse_file *ff = file->private_data;
+ bool async_dio = ff->fc->async_dio;
loff_t pos = 0;
struct inode *inode;
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);
/* optimization for short read */
- if (rw != WRITE && offset + count > i_size) {
+ if (async_dio && rw != WRITE && offset + count > i_size) {
if (offset >= i_size)
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);
@@ -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
* submission to the client filesystem if supported.
*/
- io->async = ff->fc->async_dio;
+ io->async = async_dio;
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
* synchronously.
*/
- if (!is_sync_kiocb(iocb) && (offset + count > i_size))
+ if (!is_sync_kiocb(iocb) && (offset + count > i_size) && rw == WRITE)
io->async = false;
if (rw == WRITE)