reftable/blocksource: stop using `xmmap()`

We use `xmmap()` to map reftables into memory. This function has two
problems:

  - It causes us to die in case the mmap fails.

  - It ties us to the Git codebase.

Refactor the code to use mmap(3p) instead with manual error checking.
Note that this function may not be the system-provided mmap(3p), but may
point to our `git_mmap()` wrapper that emulates the syscall on systems
that do not have mmap(3p) available.

Fix `reftable_block_source_from_file()` to properly bubble up the error
code in case the map(3p) call fails.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 8 insertions, 3 deletions

diff --git a/reftable/blocksource.c b/reftable/blocksource.c
index bba4a45b98..02972c46f4 100644
--- a/reftable/blocksource.c
+++ b/reftable/blocksource.c
@@ -98,7 +98,7 @@ static struct reftable_block_source_vtable file_vtable = {
 int reftable_block_source_from_file(struct reftable_block_source *bs,
 				    const char *name)
 {
-	struct file_block_source *p;
+	struct file_block_source *p = NULL;
 	struct stat st;
 	int fd, err;
 
@@ -122,7 +122,12 @@ int reftable_block_source_from_file(struct reftable_block_source *bs,
 	}
 
 	p->size = st.st_size;
-	p->data = xmmap(NULL, st.st_size, PROT_READ, MAP_PRIVATE, fd, 0);
+	p->data = mmap(NULL, st.st_size, PROT_READ, MAP_PRIVATE, fd, 0);
+	if (p->data == MAP_FAILED) {
+		err = REFTABLE_IO_ERROR;
+		p->data = NULL;
+		goto out;
+	}
 
 	assert(!bs->ops);
 	bs->ops = &file_vtable;
@@ -135,5 +140,5 @@ out:
 		close(fd);
 	if (err < 0)
 		reftable_free(p);
-	return 0;
+	return err;
 }