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 <[email protected]> --- 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
