From: Andre Noll <maan@systemlinux.org>
Date: Thu, 8 Dec 2011 20:01:01 +0000 (+0100)
Subject: Improve error diagnostics of mmap_full_file().
X-Git-Tag: v0.4.10~10^2
X-Git-Url: http://git.tue.mpg.de/?a=commitdiff_plain;h=d9566a07057f68b0effd404e2da7817555f35383;p=paraslash.git

Improve error diagnostics of mmap_full_file().

On mmap errors, this function used to return the error code it got
from mmap(). Unfortunately, in at least two cases, this results in
rather obscure error messages:

	$ para_afh -i .
	main: No such device
	$ touch foo; para_afh -i foo
	main: Invalid argument

This simple patch specifically checks whether the given fd refers
to a directory or an empty file so that the error messages become
more readable:

	$ para_afh -i .
	main: failed to mmap "."
	main: Is a directory
	$ touch foo; para_afh -i foo
	main: failed to mmap "foo"
	main: file is empty
---

diff --git a/afh.c b/afh.c
index f2745b61..04c13ebd 100644
--- a/afh.c
+++ b/afh.c
@@ -187,8 +187,10 @@ int main(int argc, char **argv)
 		int ret2;
 		ret = mmap_full_file(conf.inputs[i], O_RDONLY, &audio_file_data,
 			&audio_file_size, &fd);
-		if (ret < 0)
+		if (ret < 0) {
+			PARA_ERROR_LOG("failed to mmap \"%s\"\n", conf.inputs[i]);
 			goto out;
+		}
 		ret = compute_afhi(conf.inputs[i], audio_file_data, audio_file_size,
 			fd, &afhi);
 		if (ret < 0)
diff --git a/error.h b/error.h
index 63d4d5db..39c109f9 100644
--- a/error.h
+++ b/error.h
@@ -441,6 +441,7 @@ extern const char **para_errlist[];
 	PARA_ERROR(FGETS, "fgets error"), \
 	PARA_ERROR(EOF, "end of file"), \
 	PARA_ERROR(READ_PATTERN, "did not read expected pattern"), \
+	PARA_ERROR(EMPTY, "file is empty"), \
 
 
 #define ALSA_WRITE_ERRORS \
diff --git a/fd.c b/fd.c
index 2e05313e..9b6c6917 100644
--- a/fd.c
+++ b/fd.c
@@ -541,6 +541,22 @@ int mmap_full_file(const char *path, int open_mode, void **map,
 		goto out;
 	}
 	*size = file_status.st_size;
+	/*
+	 * If the file is empty, *size is zero and mmap() would return EINVAL
+	 * (Invalid argument). This error is common enough to spend an extra
+	 * error code which explicitly states the problem.
+	 */
+	ret = -E_EMPTY;
+	if (*size == 0)
+		goto out;
+	/*
+	 * If fd refers to a directory, mmap() returns ENODEV (No such device),
+	 * at least on Linux. "Is a directory" seems to be more to the point.
+	 */
+	ret = -ERRNO_TO_PARA_ERROR(EISDIR);
+	if (S_ISDIR(file_status.st_mode))
+		goto out;
+
 	ret = para_mmap(*size, mmap_prot, mmap_flags, fd, 0, map);
 out:
 	if (ret < 0 || !fd_ptr)