Re: [PATCH v4 1/4] eal: add basename function for common path manipulation

[Andre Muezerie <andremue@linux.microsoft.com>]

On Thu, Jul 31, 2025 at 04:00:38PM +0000, Bruce Richardson wrote:
> There is no standard, cross-platform function to get the basename of a
> file path across all the supported DPDK platforms, Linux, BSD and
> Windows. Both Linux and BSD have a "basename" function in standard
> library, except:
> * Linux has two different basename functions, a POSIX version (which may
>   or may not modify args), and a GNU one which is guaranteed *not* to
>   modify the input arg and returns pointer to internal storage.
> * FreeBSD has just the one basename function, but, to be different, it is
>   guaranteed *always* to modify the argument and re-use it for output.
> * Windows just doesn't have a basename function, but provides _split_path
>   as a similar function, but with many differences over basename, e.g.
>   splitting off extension, returning empty basename if path ends in "/"
>   etc. etc.
> 
> Therefore, rather than just trying to implement basename for windows,
> which opens the question as to whether to emulate GNU and *never* modify
> arg, or emulate BSD and *always* modify arg, this patchset introduces
> "rte_basename" which should have defined behaviour on all platforms. The
> patch also introduces a set of test cases to confirm consistent behaviour
> on all platforms too.
> 
> The behaviour is as in doxygen docs. Essentially:
> - does not modify input path buffer
> - returns output in a separate output buffer
> - uses snprintf and strlcpy style return value to indicate truncation
> 
> Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
> ---
>  app/test/test_string_fns.c       | 111 +++++++++++++++++++++++++++++++
>  lib/eal/include/rte_string_fns.h |  32 +++++++++
>  lib/eal/unix/meson.build         |   1 +
>  lib/eal/unix/rte_basename.c      |  37 +++++++++++
>  lib/eal/windows/meson.build      |   1 +
>  lib/eal/windows/rte_basename.c   |  53 +++++++++++++++
>  6 files changed, 235 insertions(+)
>  create mode 100644 lib/eal/unix/rte_basename.c
>  create mode 100644 lib/eal/windows/rte_basename.c
> 
> diff --git a/app/test/test_string_fns.c b/app/test/test_string_fns.c
> index 3b311325dc..1a2830575e 100644
> --- a/app/test/test_string_fns.c
> +++ b/app/test/test_string_fns.c
> @@ -205,6 +205,115 @@ test_rte_str_skip_leading_spaces(void)
>  	return 0;
>  }
>  
> +static int
> +test_rte_basename(void)
> +{
> +	/* Test case structure for positive cases */
> +	struct {
> +		const char *input_path;    /* Input path string */
> +		const char *expected;      /* Expected result */
> +	} test_cases[] = {
> +		/* Test cases from man 3 basename */
> +		{"/usr/lib", "lib"},
> +		{"/usr/", "usr"},
> +		{"usr", "usr"},
> +		{"/", "/"},
> +		{".", "."},
> +		{"..", ".."},
> +
> +		/* Additional requested test cases */
> +		{"/////", "/"},
> +		{"/path/to/file.txt", "file.txt"},
> +
> +		/* Additional edge cases with trailing slashes */
> +		{"///usr///", "usr"},
> +		{"/a/b/c/", "c"},
> +
> +		/* Empty string case */
> +		{"", "."},
> +		{NULL, "."}  /* NULL path should return "." */
> +	};
> +
> +	char buf[256];
> +	size_t result;
> +
> +	/* Run positive test cases from table */
> +	for (size_t i = 0; i < RTE_DIM(test_cases); i++) {
> +		result = rte_basename(test_cases[i].input_path, buf, sizeof(buf));
> +
> +		if (strcmp(buf, test_cases[i].expected) != 0) {
> +			LOG("FAIL [%zu]: '%s' - buf contains '%s', expected '%s'\n",
> +			    i, test_cases[i].input_path, buf, test_cases[i].expected);
> +			return -1;
> +		}
> +
> +		/* Check that the return value matches the expected string length */
> +		if (result != strlen(test_cases[i].expected)) {
> +			LOG("FAIL [%zu]: '%s' - returned length %zu, expected %zu\n",
> +			    i, test_cases[i].input_path, result, strlen(test_cases[i].expected));
> +			return -1;
> +		}
> +
> +		LOG("PASS [%zu]: '%s' -> '%s' (len=%zu)\n",
> +				i, test_cases[i].input_path, buf, result);
> +	}
> +
> +	/* re-run the table above verifying that for a NULL buffer, or zero length, we get
> +	 * correct length returned.
> +	 */
> +	for (size_t i = 0; i < RTE_DIM(test_cases); i++) {
> +		result = rte_basename(test_cases[i].input_path, NULL, 0);
> +		if (result != strlen(test_cases[i].expected)) {
> +			LOG("FAIL [%zu]: '%s' - returned length %zu, expected %zu\n",
> +			    i, test_cases[i].input_path, result, strlen(test_cases[i].expected));
> +			return -1;
> +		}
> +		LOG("PASS [%zu]: '%s' -> length %zu (NULL buffer case)\n",
> +		    i, test_cases[i].input_path, result);
> +	}
> +
> +	/* Test case: buffer too small for result should truncate and return full length */
> +	const size_t small_size = 5;
> +	result = rte_basename("/path/to/very_long_filename.txt", buf, small_size);
> +	/* Should be truncated to fit in 5 bytes (4 chars + null terminator) */
> +	if (strlen(buf) >= small_size) {
> +		LOG("FAIL: small buffer test - result '%s' not properly truncated (len=%zu, buflen=%zu)\n",
> +		    buf, strlen(buf), small_size);
> +		return -1;
> +	}
> +	/* Return value should indicate truncation occurred (>= buflen) */
> +	if (result != strlen("very_long_filename.txt")) {
> +		LOG("FAIL: small buffer test - return value %zu doesn't indicate truncation (buflen=%zu)\n",
> +		    result, small_size);
> +		return -1;
> +	}
> +	LOG("PASS: small buffer truncation -> '%s' (returned len=%zu, actual len=%zu)\n",
> +	    buf, result, strlen(buf));
> +
> +	/* extreme length test case -  check that even with paths longer than PATH_MAX we still
> +	 * return the last component correctly. Use "/zzz...zzz/abc.txt" and check we get "abc.txt"
> +	 */
> +	char basename_val[] = "abc.txt";
> +	char long_path[PATH_MAX + 50];
> +	for (int i = 0; i < PATH_MAX + 20; i++)
> +		long_path[i] = (i == 0) ? '/' : 'z';
> +	sprintf(long_path + PATH_MAX + 20, "/%s", basename_val);
> +
> +	result = rte_basename(long_path, buf, sizeof(buf));
> +	if (strcmp(buf, basename_val) != 0) {
> +		LOG("FAIL: long path test - expected '%s', got '%s'\n",
> +		    basename_val, buf);
> +		return -1;
> +	}
> +	if (result != strlen(basename_val)) {
> +		LOG("FAIL: long path test - expected length %zu, got %zu\n",
> +		    strlen(basename_val), result);
> +		return -1;
> +	}
> +	LOG("PASS: long path test -> '%s' (len=%zu)\n", buf, result);
> +	return 0;
> +}
> +
>  static int
>  test_string_fns(void)
>  {
> @@ -214,6 +323,8 @@ test_string_fns(void)
>  		return -1;
>  	if (test_rte_str_skip_leading_spaces() < 0)
>  		return -1;
> +	if (test_rte_basename() < 0)
> +		return -1;
>  	return 0;
>  }
>  
> diff --git a/lib/eal/include/rte_string_fns.h b/lib/eal/include/rte_string_fns.h
> index 702bd81251..3713c94acb 100644
> --- a/lib/eal/include/rte_string_fns.h
> +++ b/lib/eal/include/rte_string_fns.h
> @@ -149,6 +149,38 @@ rte_str_skip_leading_spaces(const char *src)
>  	return p;
>  }
>  
> +/**
> + * @warning
> + * @b EXPERIMENTAL: this API may change without prior notice.
> + *
> + * Provides the final component of a path, similar to POSIX basename function.
> + *
> + * This API provides the similar behaviour on all platforms, Linux, BSD, Windows,
> + * hiding the implementation differences.
> + * - It does not modify the input path.
> + * - The output buffer is passed as an argument, and the result is copied into it.
> + * - Expected output is the last component of the path, or the path itself if
> + *   it does not contain a directory separator.
> + * - If the final component is too long to fit in the output buffer, it will be truncated.
> + * - For empty or NULL input paths, output buffer will contain the string ".".
> + * - Supports up to PATH_MAX (BSD/Linux) or _MAX_PATH (Windows) characters in the input path.
> + *
> + * @param path
> + *   The input path string. Not modified by this function.
> + * @param buf
> + *   The buffer to hold the resultant basename.
> + *   Must be large enough to hold the result, otherwise basename will be truncated.
> + * @param buflen
> + *   The size of the buffer in bytes.
> + * @return
> + *   The number of bytes that were written to buf (excluding the terminating '\0').
> + *   If the return value is >= buflen, truncation occurred.
> + *   Return (size_t)-1 on error (Windows only)
> + */
> +__rte_experimental
> +size_t
> +rte_basename(const char *path, char *buf, size_t buflen);
> +
>  #ifdef __cplusplus
>  }
>  #endif
> diff --git a/lib/eal/unix/meson.build b/lib/eal/unix/meson.build
> index f1eb82e16a..70af352dab 100644
> --- a/lib/eal/unix/meson.build
> +++ b/lib/eal/unix/meson.build
> @@ -9,6 +9,7 @@ sources += files(
>          'eal_unix_memory.c',
>          'eal_unix_thread.c',
>          'eal_unix_timer.c',
> +        'rte_basename.c',
>          'rte_thread.c',
>  )
>  
> diff --git a/lib/eal/unix/rte_basename.c b/lib/eal/unix/rte_basename.c
> new file mode 100644
> index 0000000000..a72d6bb3c9
> --- /dev/null
> +++ b/lib/eal/unix/rte_basename.c
> @@ -0,0 +1,37 @@
> +/* SPDX-License-Identifier: BSD-3-Clause
> + * Copyright(c) 2025 Intel Corporation
> + */
> +
> +#include <string.h>
> +#include <stdlib.h>
> +#include <libgen.h>
> +#include <limits.h>
> +
> +#include <eal_export.h>
> +#include <rte_string_fns.h>
> +
> +RTE_EXPORT_EXPERIMENTAL_SYMBOL(rte_basename, 25.11)
> +size_t
> +rte_basename(const char *path, char *buf, size_t buflen)
> +{
> +	char copy[PATH_MAX + 1];
> +	size_t retval = 0;
> +
> +	if (path == NULL)
> +		return (buf == NULL) ? strlen(".") : strlcpy(buf, ".", buflen);
> +
> +	/* basename is on the end, so if path is too long, use only last PATH_MAX bytes */
> +	const size_t pathlen = strlen(path);
> +	if (pathlen > PATH_MAX)
> +		path = &path[pathlen - PATH_MAX];
> +
> +	/* make a copy of buffer since basename may modify it */
> +	strlcpy(copy, path, sizeof(copy));
> +
> +	/* if passed a null buffer, just return length of basename, otherwise strlcpy it */
> +	retval = (buf == NULL) ?
> +			strlen(basename(copy)) :
> +			strlcpy(buf, basename(copy), buflen);
> +
> +	return retval;
> +}
> diff --git a/lib/eal/windows/meson.build b/lib/eal/windows/meson.build
> index c526ede405..e7fad1f010 100644
> --- a/lib/eal/windows/meson.build
> +++ b/lib/eal/windows/meson.build
> @@ -19,6 +19,7 @@ sources += files(
>          'eal_timer.c',
>          'getline.c',
>          'getopt.c',
> +        'rte_basename.c',
>          'rte_thread.c',
>  )
>  
> diff --git a/lib/eal/windows/rte_basename.c b/lib/eal/windows/rte_basename.c
> new file mode 100644
> index 0000000000..f4dfc08a0a
> --- /dev/null
> +++ b/lib/eal/windows/rte_basename.c
> @@ -0,0 +1,53 @@
> +/* SPDX-License-Identifier: BSD-3-Clause
> + * Copyright(c) 2025 Intel Corporation
> + */
> +
> +#include <string.h>
> +#include <stdlib.h>
> +#include <rte_string_fns.h>
> +
> +size_t
> +rte_basename(const char *path, char *buf, size_t buflen)
> +{
> +	char fname[_MAX_FNAME + 1];
> +	char ext[_MAX_EXT + 1];
> +	char dir[_MAX_DIR + 1];
> +
> +	if (path == NULL || path[0] == '\0')
> +		return (buf == NULL) ? strlen(".") : strlcpy(buf, ".", buflen);
> +
> +	/* basename is on the end, so if path is too long, use only last PATH_MAX bytes */
> +	const size_t pathlen = strlen(path);
> +	if (pathlen > _MAX_PATH)
> +		path = &path[pathlen - _MAX_PATH];
> +
> +
> +	/* Use _splitpath_s to separate the path into components */
> +	int ret = _splitpath_s(path, NULL, 0, dir, sizeof(dir),
> +			fname, sizeof(fname), ext, sizeof(ext));
> +	if (ret != 0)
> +		return (size_t)-1;
> +
> +	/* if there is a trailing slash, then split_path returns no basename, but
> +	 * we want to return the last component of the path in all cases.
> +	 * Therefore re-run removing trailing slash from path.
> +	 */
> +	if (fname[0] == '\0' && ext[0] == '\0') {
> +		size_t dirlen = strlen(dir);
> +		while (dirlen > 0 && (dir[dirlen - 1] == '\\' || dir[dirlen - 1] == '/')) {
> +			/* special case for "/" to keep *nix compatibility */
> +			if (strcmp(dir, "/") == 0)
> +				return (buf == NULL) ? strlen(dir) : strlcpy(buf, dir, buflen);
> +
> +			/* Remove trailing backslash */
> +			dir[--dirlen] = '\0';
> +		}
> +		_splitpath_s(dir, NULL, 0, NULL, 0, fname, sizeof(fname), ext, sizeof(ext));
> +	}
> +
> +	if (buf == NULL)
> +		return strlen(fname) + strlen(ext);
> +
> +	/* Combine the filename and extension into output */
> +	return snprintf(buf, buflen, "%s%s", fname, ext);
> +}
> -- 
> 2.48.1

Acked-by: Andre Muezerie <andremue@linux.microsoft.com>