[PATCH v2] erofs-utils: list available compressors for help command

[Li Guifu <blucerlee@gmail.com>]

From: Gao Xiang <gaoxiang25@huawei.com>

Users can get knowledge of supported compression
algorithms then.

Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>
Signed-off-by: Li Guifu <blucerlee@gmail.com>
---
 include/erofs/compress.h |  2 ++
 lib/compressor.c         | 23 ++++++++++++++---------
 lib/compressor.h         |  1 +
 lib/compressor_lz4.c     |  1 +
 lib/compressor_lz4hc.c   |  1 +
 mkfs/main.c              | 15 +++++++++++++++
 6 files changed, 34 insertions(+), 9 deletions(-)

diff --git a/include/erofs/compress.h b/include/erofs/compress.h
index e0abb8f..fa91873 100644
--- a/include/erofs/compress.h
+++ b/include/erofs/compress.h
@@ -21,5 +21,7 @@ int erofs_write_compressed_file(struct erofs_inode *inode);
 int z_erofs_compress_init(void);
 int z_erofs_compress_exit(void);
 
+const char *z_erofs_list_available_compressors(unsigned int i);
+
 #endif
 
diff --git a/lib/compressor.c b/lib/compressor.c
index 8cc2f43..6502437 100644
--- a/lib/compressor.c
+++ b/lib/compressor.c
@@ -12,6 +12,15 @@
 
 #define EROFS_CONFIG_COMPR_DEF_BOUNDARY		(128)
 
+static struct erofs_compressor *compressors[] = {
+#if LZ4_ENABLED
+#if LZ4HC_ENABLED
+		&erofs_compressor_lz4hc,
+#endif
+		&erofs_compressor_lz4,
+#endif
+};
+
 int erofs_compress_destsize(struct erofs_compress *c,
 			    int compression_level,
 			    void *src,
@@ -36,18 +45,14 @@ int erofs_compress_destsize(struct erofs_compress *c,
 	return ret;
 }
 
+const char *z_erofs_list_available_compressors(unsigned int i)
+{
+	return (i >= ARRAY_SIZE(compressors)) ? NULL : compressors[i]->name;
+}
+
 int erofs_compressor_init(struct erofs_compress *c,
 			  char *alg_name)
 {
-	static struct erofs_compressor *compressors[] = {
-#if LZ4_ENABLED
-#if LZ4HC_ENABLED
-		&erofs_compressor_lz4hc,
-#endif
-		&erofs_compressor_lz4,
-#endif
-	};
-
 	int ret, i;
 
 	/* should be written in "minimum compression ratio * 100" */
diff --git a/lib/compressor.h b/lib/compressor.h
index 6429b2a..4b76c4c 100644
--- a/lib/compressor.h
+++ b/lib/compressor.h
@@ -14,6 +14,7 @@
 struct erofs_compress;
 
 struct erofs_compressor {
+	const char *name;
 	int default_level;
 	int best_level;
 
diff --git a/lib/compressor_lz4.c b/lib/compressor_lz4.c
index 0d33223..a9cbb80 100644
--- a/lib/compressor_lz4.c
+++ b/lib/compressor_lz4.c
@@ -39,6 +39,7 @@ static int compressor_lz4_init(struct erofs_compress *c,
 }
 
 struct erofs_compressor erofs_compressor_lz4 = {
+	.name = "lz4",
 	.default_level = 0,
 	.best_level = 0,
 	.init = compressor_lz4_init,
diff --git a/lib/compressor_lz4hc.c b/lib/compressor_lz4hc.c
index 14e0175..a160c1a 100644
--- a/lib/compressor_lz4hc.c
+++ b/lib/compressor_lz4hc.c
@@ -52,6 +52,7 @@ static int compressor_lz4hc_init(struct erofs_compress *c,
 }
 
 struct erofs_compressor erofs_compressor_lz4hc = {
+	.name = "lz4hc",
 	.default_level = LZ4HC_CLEVEL_DEFAULT,
 	.best_level = LZ4HC_CLEVEL_MAX,
 	.init = compressor_lz4hc_init,
diff --git a/mkfs/main.c b/mkfs/main.c
index 31cf1c2..1161b3f 100644
--- a/mkfs/main.c
+++ b/mkfs/main.c
@@ -29,6 +29,19 @@ static struct option long_options[] = {
 	{0, 0, 0, 0},
 };
 
+static void print_available_compressors(FILE *f, const char *delim)
+{
+	unsigned int i = 0;
+	const char *s;
+
+	while ((s = z_erofs_list_available_compressors(i)) != NULL) {
+		if (i++)
+			fputs(delim, f);
+		fputs(s, f);
+	}
+	fputc('\n', f);
+}
+
 static void usage(void)
 {
 	fprintf(stderr, "usage: [options] FILE DIRECTORY\n\n");
@@ -39,6 +52,8 @@ static void usage(void)
 	fprintf(stderr, " -EX[,...] X=extended options\n");
 	fprintf(stderr, " -T#       set a fixed UNIX timestamp # to all files\n");
 	fprintf(stderr, " --help    display this help and exit\n");
+	fprintf(stderr, "\nAvailable compressors are: ");
+	print_available_compressors(stderr, ", ");
 }
 
 static int parse_extended_opts(const char *opts)
-- 
2.17.1