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| author | Christoph Hellwig <hch@lst.de> | 2020-09-03 17:59:22 +0200 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2020-09-03 19:50:47 +0200 |
| commit | 99f667352f6c938440d9043d0f66f859d6f3d50d (patch) | |
| tree | bf5c687509f17d774cd978ac684c2a2c157d6ca2 | |
| parent | binder: print warnings when detecting oneway spamming. (diff) | |
| download | linux-99f667352f6c938440d9043d0f66f859d6f3d50d.tar.xz linux-99f667352f6c938440d9043d0f66f859d6f3d50d.zip | |
/dev/zero: also implement ->read
Christophe reported a major speedup due to avoiding the iov_iter
overhead, so just add this trivial function. Note that /dev/zero
already implements both an iter and non-iter writes so this just
makes it more symmetric.
Tested-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20200903155922.1111551-1-hch@lst.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
| -rw-r--r-- | drivers/char/mem.c | 22 |
1 files changed, 22 insertions, 0 deletions
diff --git a/drivers/char/mem.c b/drivers/char/mem.c index abd4ffdc8cde..1dc99ab15845 100644 --- a/drivers/char/mem.c +++ b/drivers/char/mem.c @@ -726,6 +726,27 @@ static ssize_t read_iter_zero(struct kiocb *iocb, struct iov_iter *iter) return written; } +static ssize_t read_zero(struct file *file, char __user *buf, + size_t count, loff_t *ppos) +{ + size_t cleared = 0; + + while (count) { + size_t chunk = min_t(size_t, count, PAGE_SIZE); + + if (clear_user(buf + cleared, chunk)) + return cleared ? cleared : -EFAULT; + cleared += chunk; + count -= chunk; + + if (signal_pending(current)) + return cleared ? cleared : -ERESTARTSYS; + cond_resched(); + } + + return cleared; +} + static int mmap_zero(struct file *file, struct vm_area_struct *vma) { #ifndef CONFIG_MMU @@ -921,6 +942,7 @@ static const struct file_operations zero_fops = { .llseek = zero_lseek, .write = write_zero, .read_iter = read_iter_zero, + .read = read_zero, .write_iter = write_iter_zero, .mmap = mmap_zero, .get_unmapped_area = get_unmapped_area_zero, |