[PATCH 2/2] makedumpfile: Fix --dry-run for incomplete dumps

[Philipp Rudo]

When running out of space during a dry run, e.g. by limiting the output
size using the -L option, makedumpfile fails with

	[...]
	Can't write the dump file(vmcore). Size limit(104857600) reached.
	get_nr_pages: Can't seek end of the dump file(vmcore).
	__read_disk_dump_header: Can't open a file(vmcore). No such file or directory
	[...]

This is because for --dry-run no dump file is created and a dummy file
descriptor of -1 is used. Thus the file operations in get_nr_pages and
check_and_modify_*_headers fail. Fix the first error by using
write_bytes as file size for the output file and the second one by
always returning TRUE for check_and_modify_headers.

Fixes: 3422e1d ("[PATCH 1/2] Add --dry-run option to prevent writing the dumpfile")
Signed-off-by: Philipp Rudo <prudo at redhat.com>
---
 makedumpfile.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/makedumpfile.c b/makedumpfile.c
index 30f9725..c063267 100644
--- a/makedumpfile.c
+++ b/makedumpfile.c
@@ -5113,6 +5113,9 @@ check_and_modify_multiple_kdump_headers() {
 int
 check_and_modify_headers()
 {
+	if (info->flag_dry_run)
+		return TRUE;
+
 	if (info->flag_elf_dumpfile)
 		return check_and_modify_elf_headers(info->name_dumpfile);
 	else
@@ -7996,7 +7999,11 @@ get_nr_pages(void *buf, struct cache_data *cd_page){
 	int size, file_end, nr_pages;
 	page_desc_t *pd = buf;
 
-	file_end = lseek(cd_page->fd, 0, SEEK_END);
+	if (info->flag_dry_run)
+		file_end = write_bytes;
+	else
+		file_end = lseek(cd_page->fd, 0, SEEK_END);
+
 	if (file_end < 0) {
 		ERRMSG("Can't seek end of the dump file(%s).\n", cd_page->file_name);
 		return -1;
-- 
2.31.1