Re: [PATCH v4 05/11] seq_buf: Add seq_buf_strlen()
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From: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Date: 2026-10-03 15:37:02
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On Fri, Oct 02, 2026 at 08:59:10PM -0700, Kees Cook wrote:
Several strlcat() call sites being converted to seq_buf need behavior seq_buf doesn't currently provide. The return from seq_buf_used() is not the length of the string in a seq_buf. Once the buffer is full or has overflowed it returns the buffer size, which counts the byte that seq_buf_str() replaces with the NUL, so a caller that needs the string and its length has to call seq_buf_str() and then walk the string with strlen(). Move the termination out of seq_buf_str() into a helper that returns where it put the NUL, and add seq_buf_strlen(), which terminates the buffer in the same way and returns that offset. As discussed in review, don't add WARN_ON() for seq_buf_strlen() and drop it from seq_buf_str(). Add tests comparing seq_buf_strlen() against strlen() of seq_buf_str() for empty, appended, truncated, exactly full, and overflowed buffers, checking that seq_buf_strlen() alone terminates a full buffer, and checking that a zero-sized seq_buf reports an empty string from both accessors without touching the buffer. Tests passed under qemu on ARCH=x86_64 with GCC 16.2.0 and CONFIG_KASAN=y, and on big-endian ARCH=s390 with GCC s390x-linux-gnu 16.2.0.
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static inline const char *seq_buf_str(struct seq_buf *s) { - if (WARN_ON(s->size == 0)) + if (s->size == 0) return ""; - if (seq_buf_buffer_left(s)) - s->buffer[s->len] = 0; - else - s->buffer[s->size - 1] = 0; + __seq_buf_terminate(s); return s->buffer; }
Looking at this again, can't it be rewritten now using _strlen()? if (seq_buf_strlen(s)) return s->buffer; return ""; ? ...
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+static inline size_t seq_buf_strlen(struct seq_buf *s) +{ + if (s->size == 0) + return 0; + + return __seq_buf_terminate(s); +}
(Left for the context to the above.) -- With Best Regards, Andy Shevchenko