add new system file

hc

2024-02-20 102a0743326a03cd1a1202ceda21e175b7d3575c

 kernel/drivers/tty/vt/vc_screen.c
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@@ -386,10 +386,6 @@
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 	uni_mode = use_unicode(inode);
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 	attr = use_attributes(inode);
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-	ret = -ENXIO;
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-	vc = vcs_vc(inode, &viewed);
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-	if (!vc)
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-		goto unlock_out;
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 	ret = -EINVAL;
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 	if (pos < 0)
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@@ -407,16 +403,20 @@
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 		unsigned int this_round, skip = 0;
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 		int size;
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+		vc = vcs_vc(inode, &viewed);
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+		if (!vc) {
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+			ret = -ENXIO;
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+			break;
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+		}
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+
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 		/* Check whether we are above size each round,
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 		 * as copy_to_user at the end of this loop
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 		 * could sleep.
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 		 */
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 		size = vcs_size(vc, attr, uni_mode);
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 		if (size < 0) {
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-			if (read)
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-				break;
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 			ret = size;
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-			goto unlock_out;
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+			break;
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 		}
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 		if (pos >= size)
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 			break;
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@@ -656,10 +656,17 @@
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 			}
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 		}
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-		/* The vcs_size might have changed while we slept to grab
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-		 * the user buffer, so recheck.
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+		/* The vc might have been freed or vcs_size might have changed
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+		 * while we slept to grab the user buffer, so recheck.
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 		 * Return data written up to now on failure.
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 		 */
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+		vc = vcs_vc(inode, &viewed);
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+		if (!vc) {
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+			if (written)
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+				break;
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+			ret = -ENXIO;
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+			goto unlock_out;
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+		}
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 		size = vcs_size(vc, attr, false);
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 		if (size < 0) {
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 			if (written)