Filesystems that generic_file_read_iter will not be allowed to perform
non-blocking reads. This only will read data if it's in the page cache and if
there is no page error (causing a re-read).
Signed-off-by: Milosz Tanski <milosz@xxxxxxxxx>
---
fs/read_write.c | 4 +++-
include/linux/fs.h | 3 +++
mm/filemap.c | 19 +++++++++++++++++++
3 files changed, 25 insertions(+), 1 deletion(-)
diff --git a/fs/read_write.c b/fs/read_write.c
index 3db2e87..29b5823 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -864,8 +864,10 @@ ssize_t vfs_readv(struct file *file, const struct iovec __user *vec,
return -EBADF;
if (!(file->f_mode & FMODE_CAN_READ))
return -EINVAL;
- if (flags & ~0)
+ if (flags & ~RWF_NONBLOCK)
return -EINVAL;
+ if ((file->f_flags & O_DIRECT) && (flags & RWF_NONBLOCK))
+ return -EAGAIN;
return do_readv_writev(READ, file, vec, vlen, pos, flags);
}
diff --git a/include/linux/fs.h b/include/linux/fs.h
index e9bea52..c9c6ac5 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1477,6 +1477,9 @@ struct block_device_operations;
#define HAVE_COMPAT_IOCTL 1
#define HAVE_UNLOCKED_IOCTL 1
+/* These flags are used for the readv/writev syscalls with flags. */
+#define RWF_NONBLOCK O_NONBLOCK
+
struct iov_iter;
struct file_operations {
diff --git a/mm/filemap.c b/mm/filemap.c
index e0919ba..6b7aba8 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1483,7 +1483,10 @@ static ssize_t do_generic_file_read(struct file *filp, loff_t *ppos,
cond_resched();
find_page:
page = find_get_page(mapping, index);
+
if (!page) {
+ if (flags & RWF_NONBLOCK)
+ goto would_block;
page_cache_sync_readahead(mapping,
ra, filp,
index, last_index - index);
@@ -1575,6 +1578,11 @@ page_ok:
continue;
page_not_up_to_date:
+ if (flags & RWF_NONBLOCK) {
+ page_cache_release(page);
+ goto would_block;
+ }
+
/* Get exclusive access to the page ... */
error = lock_page_killable(page);
if (unlikely(error))
@@ -1594,6 +1602,12 @@ page_not_up_to_date_locked:
goto page_ok;
}
+ if (flags & RWF_NONBLOCK) {
+ unlock_page(page);
+ page_cache_release(page);
+ goto would_block;
+ }
+
readpage:
/*
* A previous I/O error may have been due to temporary
@@ -1664,6 +1678,8 @@ no_cached_page:
goto readpage;
}
+would_block:
+ error = -EAGAIN;
out:
ra->prev_pos = prev_index;
ra->prev_pos <<= PAGE_CACHE_SHIFT;
@@ -1697,6 +1713,9 @@ generic_file_read_iter(struct kiocb *iocb, struct iov_iter *iter)
size_t count = iov_iter_count(iter);
loff_t size;
+ if (iocb->ki_rwflags & RWF_NONBLOCK)
+ return -EAGAIN;
+
if (!count)
goto out; /* skip atime */
size = i_size_read(inode);
--
2.1.0
--
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