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/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>
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1 changed files with 22 additions and 0 deletions
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@ -726,6 +726,27 @@ static ssize_t read_iter_zero(struct kiocb *iocb, struct iov_iter *iter)
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return written;
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}
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static ssize_t read_zero(struct file *file, char __user *buf,
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size_t count, loff_t *ppos)
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{
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size_t cleared = 0;
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while (count) {
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size_t chunk = min_t(size_t, count, PAGE_SIZE);
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if (clear_user(buf + cleared, chunk))
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return cleared ? cleared : -EFAULT;
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cleared += chunk;
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count -= chunk;
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if (signal_pending(current))
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return cleared ? cleared : -ERESTARTSYS;
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cond_resched();
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}
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return cleared;
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}
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static int mmap_zero(struct file *file, struct vm_area_struct *vma)
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{
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#ifndef CONFIG_MMU
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@ -921,6 +942,7 @@ static const struct file_operations zero_fops = {
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.llseek = zero_lseek,
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.write = write_zero,
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.read_iter = read_iter_zero,
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.read = read_zero,
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.write_iter = write_iter_zero,
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.mmap = mmap_zero,
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.get_unmapped_area = get_unmapped_area_zero,
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