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 ++--
mm/filemap.c | 21 +++++++++++++++++++++
2 files changed, 23 insertions(+), 2 deletions(-)
diff --git a/fs/read_write.c b/fs/read_write.c
index 6c5030a..87a6034 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -908,7 +908,7 @@ SYSCALL_DEFINE4(readv2, unsigned long, fd, const struct iovec __user *, vec,
struct fd f = fdget_pos(fd);
ssize_t ret = -EBADF;
- if (flags & ~0)
+ if (flags & ~O_NONBLOCK)
return -EINVAL;
if (f.file) {
@@ -1006,7 +1006,7 @@ SYSCALL_DEFINE6(preadv2, unsigned long, fd, const struct iovec __user *, vec,
struct fd f;
ssize_t ret = -EBADF;
- if (flags & ~0)
+ if (flags & ~O_NONBLOCK)
return -EINVAL;
if (pos < 0)
return -EINVAL;
diff --git a/mm/filemap.c b/mm/filemap.c
index c95edbf..5b72572 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 & O_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 & O_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 & O_NONBLOCK) {
+ unlock_page(page);
+ page_cache_release(page);
+ goto would_block;
+ }
+
readpage:
/*
* A previous I/O error may have been due to temporary
@@ -1662,6 +1676,10 @@ no_cached_page:
goto out;
}
goto readpage;
+
+would_block:
+ error = -EAGAIN;
+ goto out;
}
out:
@@ -1697,6 +1715,9 @@ generic_file_read_iter(struct kiocb *iocb, struct iov_iter *iter, int flags)
size_t count = iov_iter_count(iter);
loff_t size;
+ if (flags & O_NONBLOCK)
+ return -EAGAIN;
+
if (!count)
goto out; /* skip atime */
size = i_size_read(inode);
--
1.7.9.5
--
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