Add a "zstream decompress" subcommand

It can be used to repair a ZFS file system corrupted by ZFS bug openzfs#12762.
Use it like this:

zfs send -c <DS> | \
zstream decompress <OBJECT>,<OFFSET>[,<COMPRESSION_ALGO>] ... | \
zfs recv <DST_DS>

Reviewed-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Allan Jude <allan@klarasystems.com>
Signed-off-by: Alan Somers <asomers@gmail.com>
Sponsored-by:  Axcient
Workaround for openzfs#12762
Closes openzfs#13256

cmd/zstream/Makefile.am

@@ -4,13 +4,15 @@ CPPCHECKTARGETS += zstream
 zstream_SOURCES = \
 	%D%/zstream.c \
 	%D%/zstream.h \
+	%D%/zstream_decompress.c \
 	%D%/zstream_dump.c \
 	%D%/zstream_redup.c \
 	%D%/zstream_token.c
 
 zstream_LDADD = \
 	libzfs.la \
 	libzfs_core.la \
+	libzpool.la \
 	libnvpair.la
 
 PHONY += install-exec-hook

cmd/zstream/zstream.c

@@ -40,6 +40,8 @@ zstream_usage(void)
 	    "\tzstream dump [-vCd] FILE\n"
 	    "\t... | zstream dump [-vCd]\n"
 	    "\n"
+	    "\tzstream decompress [-v] [OBJECT,OFFSET[,TYPE]] ...\n"
+	    "\n"
 	    "\tzstream token resume_token\n"
 	    "\n"
 	    "\tzstream redup [-v] FILE | ...\n");
@@ -61,6 +63,8 @@ main(int argc, char *argv[])
 
 	if (strcmp(subcommand, "dump") == 0) {
 		return (zstream_do_dump(argc - 1, argv + 1));
+	} else if (strcmp(subcommand, "decompress") == 0) {
+		return (zstream_do_decompress(argc - 1, argv + 1));
 	} else if (strcmp(subcommand, "token") == 0) {
 		return (zstream_do_token(argc - 1, argv + 1));
 	} else if (strcmp(subcommand, "redup") == 0) {

cmd/zstream/zstream.h

@@ -24,8 +24,12 @@
 extern "C" {
 #endif
 
+extern void *safe_calloc(size_t n);
+extern int sfread(void *buf, size_t size, FILE *fp);
+extern void *safe_malloc(size_t size);
 extern int zstream_do_redup(int, char *[]);
 extern int zstream_do_dump(int, char *[]);
+extern int zstream_do_decompress(int argc, char *argv[]);
 extern int zstream_do_token(int, char *[]);
 extern void zstream_usage(void);