From: Michael Haggerty <mhagger@alum.mit.edu>
To: Junio C Hamano <gitster@pobox.com>
Cc: Kim Gybels <kgybels@infogroep.be>,
Johannes Schindelin <johannes.schindelin@gmx.de>,
Jeff King <peff@peff.net>,
git@vger.kernel.org, Michael Haggerty <mhagger@alum.mit.edu>
Subject: [PATCH 5/6] load_contents(): don't try to mmap an empty file
Date: Wed, 24 Jan 2018 12:14:15 +0100 [thread overview]
Message-ID: <f06611f06a8b01843bd71cd9fedec0f1eb0ee551.1516791909.git.mhagger@alum.mit.edu> (raw)
In-Reply-To: <cea5e366-dc95-6f41-6373-f8bbef103561@alum.mit.edu>
In-Reply-To: <cover.1516791909.git.mhagger@alum.mit.edu>
We don't actually create zero-length `packed-refs` files, but they are
valid and we should handle them correctly. The old code `xmmap()`ed
such files, which led to an error when `munmap()` was called. So, if
the `packed-refs` file is empty, leave the snapshot at its zero values
and return 0 without trying to read or mmap the file.
Returning 0 also makes `create_snapshot()` exit early, which avoids
the technically undefined comparison `NULL < NULL`.
Reported-by: Kim Gybels <kgybels@infogroep.be>
Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
---
refs/packed-backend.c | 13 ++++++-------
1 file changed, 6 insertions(+), 7 deletions(-)
diff --git a/refs/packed-backend.c b/refs/packed-backend.c
index 988c45402b..e829cf206d 100644
--- a/refs/packed-backend.c
+++ b/refs/packed-backend.c
@@ -461,7 +461,8 @@ static void verify_buffer_safe(struct snapshot *snapshot)
/*
* Depending on `mmap_strategy`, either mmap or read the contents of
* the `packed-refs` file into the snapshot. Return 1 if the file
- * existed and was read, or 0 if the file was absent. Die on errors.
+ * existed and was read, or 0 if the file was absent or empty. Die on
+ * errors.
*/
static int load_contents(struct snapshot *snapshot)
{
@@ -492,19 +493,17 @@ static int load_contents(struct snapshot *snapshot)
die_errno("couldn't stat %s", snapshot->refs->path);
size = xsize_t(st.st_size);
- switch (mmap_strategy) {
- case MMAP_NONE:
+ if (!size) {
+ return 0;
+ } else if (mmap_strategy == MMAP_NONE) {
snapshot->buf = xmalloc(size);
bytes_read = read_in_full(fd, snapshot->buf, size);
if (bytes_read < 0 || bytes_read != size)
die_errno("couldn't read %s", snapshot->refs->path);
snapshot->mmapped = 0;
- break;
- case MMAP_TEMPORARY:
- case MMAP_OK:
+ } else {
snapshot->buf = xmmap(NULL, size, PROT_READ, MAP_PRIVATE, fd, 0);
snapshot->mmapped = 1;
- break;
}
close(fd);
--
2.14.2
next prev parent reply other threads:[~2018-01-24 11:14 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-13 16:11 [PATCH] packed_ref_cache: don't use mmap() for small files Kim Gybels
2018-01-13 18:56 ` Johannes Schindelin
2018-01-14 19:14 ` [PATCH v2] " Kim Gybels
2018-01-15 12:17 ` [PATCH 0/3] Supplements to "packed_ref_cache: don't use mmap() for small files" Michael Haggerty
2018-01-15 12:17 ` [PATCH 1/3] SQUASH? Mention that `snapshot::buf` can be NULL for empty files Michael Haggerty
2018-01-15 12:17 ` [PATCH 2/3] create_snapshot(): exit early if the file was empty Michael Haggerty
2018-01-15 12:17 ` [PATCH 3/3] find_reference_location(): don't invoke if `snapshot->buf` is NULL Michael Haggerty
2018-01-17 20:23 ` [PATCH 0/3] Supplements to "packed_ref_cache: don't use mmap() for small files" Johannes Schindelin
2018-01-17 21:52 ` Junio C Hamano
2018-01-15 21:15 ` [PATCH] packed_ref_cache: don't use mmap() for small files Jeff King
2018-01-15 23:37 ` Kim Gybels
2018-01-15 23:52 ` Jeff King
2018-01-16 19:38 ` [PATCH v3] " Kim Gybels
2018-01-17 22:09 ` Jeff King
2018-01-21 4:41 ` Michael Haggerty
2018-01-22 19:31 ` Junio C Hamano
2018-01-24 11:05 ` Michael Haggerty
2018-01-24 11:14 ` [PATCH 0/6] Yet another approach to handling empty snapshots Michael Haggerty
2018-01-24 11:14 ` [PATCH 1/6] struct snapshot: store `start` rather than `header_len` Michael Haggerty
2018-01-24 20:36 ` Jeff King
2018-01-24 11:14 ` [PATCH 2/6] create_snapshot(): use `xmemdupz()` rather than a strbuf Michael Haggerty
2018-01-24 11:14 ` [PATCH 3/6] find_reference_location(): make function safe for empty snapshots Michael Haggerty
2018-01-24 20:27 ` Jeff King
2018-01-24 21:11 ` Junio C Hamano
2018-01-24 21:34 ` Jeff King
2018-01-24 11:14 ` [PATCH 4/6] packed_ref_iterator_begin(): make optimization more general Michael Haggerty
2018-01-24 20:32 ` Jeff King
2018-01-24 11:14 ` Michael Haggerty [this message]
2018-01-24 11:14 ` [PATCH 6/6] packed_ref_cache: don't use mmap() for small files Michael Haggerty
2018-01-24 20:38 ` [PATCH 0/6] Yet another approach to handling empty snapshots Jeff King
2018-01-24 20:54 ` Junio C Hamano
2018-02-15 16:54 ` Johannes Schindelin
2018-01-24 18:05 ` [PATCH v3] packed_ref_cache: don't use mmap() for small files Junio C Hamano
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