The strcpy call in open_output_fd() implies that the output buffer
must be at least 25 chars long. And it's true. The only caller that
can trigger that code is checkout-index, which has the buffer of
PATH_MAX chars (and any systems that have PATH_MAX shorter than 25
chars are just insane).

But in order to say that, one has to walk through a dozen of
functions. Just convert it to strbuf to avoid the constraint and
confusion.

Although my original motivation was simpler than that. I just wanted
to change "char *path" to "const char *path" in checkout_entry() to
make sure no funny business regarding "path" in that function.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclo...@gmail.com>
---
 builtin/checkout-index.c | 19 ++++++++++++-------
 cache.h                  |  2 +-
 entry.c                  | 29 ++++++++++++++++-------------
 3 files changed, 29 insertions(+), 21 deletions(-)

diff --git a/builtin/checkout-index.c b/builtin/checkout-index.c
index 69e167b..6d88c0c 100644
--- a/builtin/checkout-index.c
+++ b/builtin/checkout-index.c
@@ -14,7 +14,12 @@
 static int line_termination = '\n';
 static int checkout_stage; /* default to checkout stage0 */
 static int to_tempfile;
-static char topath[4][PATH_MAX + 1];
+static struct strbuf topath[4] = {
+       STRBUF_INIT,
+       STRBUF_INIT,
+       STRBUF_INIT,
+       STRBUF_INIT
+};
 
 static struct checkout state;
 
@@ -26,19 +31,19 @@ static void write_tempfile_record(const char *name, int 
prefix_length)
                for (i = 1; i < 4; i++) {
                        if (i > 1)
                                putchar(' ');
-                       if (topath[i][0])
-                               fputs(topath[i], stdout);
+                       if (topath[i].len)
+                               fputs(topath[i].buf, stdout);
                        else
                                putchar('.');
                }
        } else
-               fputs(topath[checkout_stage], stdout);
+               fputs(topath[checkout_stage].buf, stdout);
 
        putchar('\t');
        write_name_quoted(name + prefix_length, stdout, line_termination);
 
        for (i = 0; i < 4; i++) {
-               topath[i][0] = 0;
+               strbuf_reset(&topath[i]);
        }
 }
 
@@ -65,7 +70,7 @@ static int checkout_file(const char *name, int prefix_length)
                        continue;
                did_checkout = 1;
                if (checkout_entry(ce, &state,
-                   to_tempfile ? topath[ce_stage(ce)] : NULL) < 0)
+                   to_tempfile ? &topath[ce_stage(ce)] : NULL) < 0)
                        errs++;
        }
 
@@ -109,7 +114,7 @@ static void checkout_all(const char *prefix, int 
prefix_length)
                                write_tempfile_record(last_ce->name, 
prefix_length);
                }
                if (checkout_entry(ce, &state,
-                   to_tempfile ? topath[ce_stage(ce)] : NULL) < 0)
+                   to_tempfile ? &topath[ce_stage(ce)] : NULL) < 0)
                        errs++;
                last_ce = ce;
        }
diff --git a/cache.h b/cache.h
index 51d6602..276182f 100644
--- a/cache.h
+++ b/cache.h
@@ -962,7 +962,7 @@ struct checkout {
                 refresh_cache:1;
 };
 
-extern int checkout_entry(struct cache_entry *ce, const struct checkout 
*state, char *topath);
+extern int checkout_entry(struct cache_entry *ce, const struct checkout 
*state, struct strbuf *topath);
 
 struct cache_def {
        char path[PATH_MAX + 1];
diff --git a/entry.c b/entry.c
index d955af5..a76942d 100644
--- a/entry.c
+++ b/entry.c
@@ -92,15 +92,15 @@ static void *read_blob_entry(const struct cache_entry *ce, 
unsigned long *size)
        return NULL;
 }
 
-static int open_output_fd(char *path, const struct cache_entry *ce, int 
to_tempfile)
+static int open_output_fd(struct strbuf *path, const struct cache_entry *ce, 
int to_tempfile)
 {
        int symlink = (ce->ce_mode & S_IFMT) != S_IFREG;
        if (to_tempfile) {
-               strcpy(path, symlink
-                      ? ".merge_link_XXXXXX" : ".merge_file_XXXXXX");
-               return mkstemp(path);
+               strbuf_reset(path);
+               strbuf_addstr(path, symlink ? ".merge_link_XXXXXX" : 
".merge_file_XXXXXX");
+               return mkstemp(path->buf);
        } else {
-               return create_file(path, !symlink ? ce->ce_mode : 0666);
+               return create_file(path->buf, !symlink ? ce->ce_mode : 0666);
        }
 }
 
@@ -115,7 +115,7 @@ static int fstat_output(int fd, const struct checkout 
*state, struct stat *st)
        return 0;
 }
 
-static int streaming_write_entry(const struct cache_entry *ce, char *path,
+static int streaming_write_entry(const struct cache_entry *ce, struct strbuf 
*path,
                                 struct stream_filter *filter,
                                 const struct checkout *state, int to_tempfile,
                                 int *fstat_done, struct stat *statbuf)
@@ -132,12 +132,12 @@ static int streaming_write_entry(const struct cache_entry 
*ce, char *path,
        result |= close(fd);
 
        if (result)
-               unlink(path);
+               unlink(path->buf);
        return result;
 }
 
 static int write_entry(struct cache_entry *ce,
-                      char *path, const struct checkout *state, int 
to_tempfile)
+                      struct strbuf *path_buf, const struct checkout *state, 
int to_tempfile)
 {
        unsigned int ce_mode_s_ifmt = ce->ce_mode & S_IFMT;
        int fd, ret, fstat_done = 0;
@@ -146,15 +146,17 @@ static int write_entry(struct cache_entry *ce,
        unsigned long size;
        size_t wrote, newsize = 0;
        struct stat st;
+       const char *path;
 
        if (ce_mode_s_ifmt == S_IFREG) {
                struct stream_filter *filter = get_stream_filter(ce->name, 
ce->sha1);
                if (filter &&
-                   !streaming_write_entry(ce, path, filter,
+                   !streaming_write_entry(ce, path_buf, filter,
                                           state, to_tempfile,
                                           &fstat_done, &st))
                        goto finish;
        }
+       path = path_buf->buf;
 
        switch (ce_mode_s_ifmt) {
        case S_IFREG:
@@ -183,7 +185,8 @@ static int write_entry(struct cache_entry *ce,
                        size = newsize;
                }
 
-               fd = open_output_fd(path, ce, to_tempfile);
+               fd = open_output_fd(path_buf, ce, to_tempfile);
+               path = path_buf->buf;
                if (fd < 0) {
                        free(new);
                        return error("unable to create file %s (%s)",
@@ -235,10 +238,10 @@ static int check_path(const char *path, int len, struct 
stat *st, int skiplen)
 }
 
 int checkout_entry(struct cache_entry *ce,
-                  const struct checkout *state, char *topath)
+                  const struct checkout *state, struct strbuf *topath)
 {
        static struct strbuf path_buf = STRBUF_INIT;
-       char *path;
+       const char *path;
        struct stat st;
        int len;
 
@@ -278,5 +281,5 @@ int checkout_entry(struct cache_entry *ce,
        } else if (state->not_new)
                return 0;
        create_directories(path, len, state);
-       return write_entry(ce, path, state, 0);
+       return write_entry(ce, &path_buf, state, 0);
 }
-- 
1.8.2.83.gc99314b

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