[PATCH v2] erofs-utils: lib: fix infinite loop on EOF in erofs_io_xcopy

[Ajay Rajera <newajay.11r@gmail.com>]

erofs_io_xcopy() has a fallback do-while loop for when the
kernel fast-paths (copy_file_range/sendfile) do not handle all
the data.  The loop does:

    ret = erofs_io_read(vin, buf, ret);
    if (ret < 0)
        return ret;
    if (ret > 0) { ... pos += ret; }
    len -= ret;
  } while (len);

When erofs_io_read() returns 0 (EOF -- source exhausted before
all bytes were copied), only the ret < 0 and ret > 0 branches
were handled.  Since ret == 0, `len -= ret` is a no-op and
`while (len)` stays true, causing the loop to spin forever at
100% CPU with no error and no progress.

This can be triggered when building an EROFS image from an input
file that is shorter than expected -- e.g. a truncated source
file, a pipe/FIFO that closes early, or a file being modified
concurrently during mkfs.

Fix it by treating a zero return as an error (-EIO) so the
caller fails cleanly instead of hanging indefinitely.

Also fix the long-standing 'pading' -> 'padding' typo in the
short-read diagnostic message of erofs_dev_read().

Signed-off-by: Ajay Rajera <newajay.11r@gmail.com>
---
v2:
 - Use a cleaner if/else if structure instead of nested ifs (Lucas)
 - Return -EIO instead of -ENODATA on premature EOF as it represents an I/O issue (Lucas)
Signed-off-by: Ajay Rajera <newajay.11r@gmail.com>
---
 lib/io.c | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/lib/io.c b/lib/io.c
index 0c5eb2c..cb99dee 100644
--- a/lib/io.c
+++ b/lib/io.c
@@ -430,7 +430,7 @@ ssize_t erofs_dev_read(struct erofs_sb_info *sbi, int device_id,
 	if (read < 0)
 		return read;
 	if (read < len) {
-		erofs_info("reach EOF of device @ %llu, pading with zeroes",
+		erofs_info("reach EOF of device @ %llu, padding with zeroes",
 			   offset | 0ULL);
 		memset(buf + read, 0, len - read);
 	}
@@ -667,12 +667,13 @@ int erofs_io_xcopy(struct erofs_vfile *vout, off_t pos,
 		ret = erofs_io_read(vin, buf, ret);
 		if (ret < 0)
 			return ret;
-		if (ret > 0) {
-			ret = erofs_io_pwrite(vout, buf, pos, ret);
-			if (ret < 0)
-				return ret;
-			pos += ret;
-		}
+		else if (!ret)
+			return -EIO;
+
+		ret = erofs_io_pwrite(vout, buf, pos, ret);
+		if (ret < 0)
+			return ret;
+		pos += ret;
 		len -= ret;
 	} while (len);
 	return 0;
-- 
2.51.0.windows.1