Introduce for_each_recent_reflog_ent().

This can be used to scan only the last few kilobytes of a reflog, as a
cheap optimization when the data you are looking for is likely to be
found near the end of it.  The caller is expected to fall back to the
full scan if that is not the case.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/refs.c b/refs.c
index 33ced65a7801f8653d608a9580e237ce8df39ae2..024211d72b5e21e1c87e98b0f7e3a6982525d82d 100644 (file)
--- a/refs.c
+++ b/refs.c
@@ -1453,7 +1453,7 @@ int read_ref_at(const char *ref, unsigned long at_time, int cnt, unsigned char *
        return 1;
 }
 
-int for_each_reflog_ent(const char *ref, each_reflog_ent_fn fn, void *cb_data)
+int for_each_recent_reflog_ent(const char *ref, each_reflog_ent_fn fn, long ofs, void *cb_data)
 {
        const char *logfile;
        FILE *logfp;
@@ -1464,6 +1464,16 @@ int for_each_reflog_ent(const char *ref, each_reflog_ent_fn fn, void *cb_data)
        logfp = fopen(logfile, "r");
        if (!logfp)
                return -1;
+
+       if (ofs) {
+               struct stat statbuf;
+               if (fstat(fileno(logfp), &statbuf) ||
+                   statbuf.st_size < ofs ||
+                   fseek(logfp, -ofs, SEEK_END) ||
+                   fgets(buf, sizeof(buf), logfp))
+                       return -1;
+       }
+
        while (fgets(buf, sizeof(buf), logfp)) {
                unsigned char osha1[20], nsha1[20];
                char *email_end, *message;
@@ -1497,6 +1507,11 @@ int for_each_reflog_ent(const char *ref, each_reflog_ent_fn fn, void *cb_data)
        return ret;
 }
 
+int for_each_reflog_ent(const char *ref, each_reflog_ent_fn fn, void *cb_data)
+{
+       return for_each_recent_reflog_ent(ref, fn, 0, cb_data);
+}
+
 static int do_for_each_reflog(const char *base, each_ref_fn fn, void *cb_data)
 {
        DIR *dir = opendir(git_path("logs/%s", base));

diff --git a/refs.h b/refs.h
index 06ad26055661a9b9e475d0f8a7bd6d1cfb42e792..3bb529d3870012feda9a0398cba15c09aee10cf9 100644 (file)
--- a/refs.h
+++ b/refs.h
@@ -60,6 +60,7 @@ extern int read_ref_at(const char *ref, unsigned long at_time, int cnt, unsigned
 /* iterate over reflog entries */
 typedef int each_reflog_ent_fn(unsigned char *osha1, unsigned char *nsha1, const char *, unsigned long, int, const char *, void *);
 int for_each_reflog_ent(const char *ref, each_reflog_ent_fn fn, void *cb_data);
+int for_each_recent_reflog_ent(const char *ref, each_reflog_ent_fn fn, long, void *cb_data);
 
 /*
  * Calls the specified function for each reflog file until it returns nonzero,

diff --git a/sha1_name.c b/sha1_name.c
index 4c0370bb796eb7bd69992e1d09cc5ae98df16881..38c9f1b19e89401b24204b4daac26f327a8f8d8f 100644 (file)
--- a/sha1_name.c
+++ b/sha1_name.c
@@ -775,7 +775,13 @@ int interpret_nth_last_branch(const char *name, struct strbuf *buf)
                strbuf_init(&cb.buf[i], 20);
        cb.cnt = 0;
        retval = 0;
-       for_each_reflog_ent("HEAD", grab_nth_branch_switch, &cb);
+       for_each_recent_reflog_ent("HEAD", grab_nth_branch_switch, 40960, &cb);
+       if (cb.cnt < nth) {
+               cb.cnt = 0;
+               for (i = 0; i < nth; i++)
+                       strbuf_release(&cb.buf[i]);
+               for_each_reflog_ent("HEAD", grab_nth_branch_switch, &cb);
+       }
        if (cb.cnt < nth)
                goto release_return;
        i = cb.cnt % nth;