Merge branch 'np/delta' into next

* np/delta:
  split the diff-delta interface
  Document the configuration file
  Document git-var -l listing also configuration variables
  rev-parse: better error message for ambiguous arguments

8 files changed, 367 insertions, 109 deletions

diff --git a/Documentation/config.txt b/Documentation/config.txt
new file mode 100644
index 0000000000..b27b0d5c06
--- /dev/null
+++ b/Documentation/config.txt
@@ -0,0 +1,181 @@
+CONFIGURATION FILE
+------------------
+
+The git configuration file contains a number of variables that affect
+the git commands behaviour. They can be used by both the git plumbing
+and the porcelains. The variables are divided to sections, where
+in the fully qualified variable name the variable itself is the last
+dot-separated segment and the section name is everything before the last
+dot. The variable names are case-insensitive and only alphanumeric
+characters are allowed. Some variables may appear multiple times.
+
+The syntax is fairly flexible and permissive; whitespaces are mostly
+ignored. The '#' and ';' characters begin commends to the end of line,
+blank lines are ignored, lines containing strings enclosed in square
+brackets start sections and all the other lines are recognized
+as setting variables, in the form 'name = value'. If there is no equal
+sign on the line, the entire line is taken as 'name' and the variable
+is recognized as boolean "true". String values may be entirely or partially
+enclosed in double quotes; some variables may require special value format.
+
+Example
+~~~~~~~
+
+	# Core variables
+	[core]
+		; Don't trust file modes
+		filemode = false
+
+	# Our diff algorithm
+	[diff]
+		external = "/usr/local/bin/gnu-diff -u"
+		renames = true
+
+Variables
+~~~~~~~~~
+
+Note that this list is non-comprehensive and not necessarily complete.
+For command-specific variables, you will find more detailed description
+in the appropriate manual page. You will find description of non-core
+porcelain configuration variables in the respective porcelain documentation.
+
+core.fileMode::
+	If false, the executable bit differences between the index and
+	the working copy are ignored; useful on broken filesystems like FAT.
+	See gitlink:git-update-index[1]. True by default.
+
+core.gitProxy::
+	A "proxy command" to execute (as 'command host port') instead
+	of establishing direct connection to the remote server when
+	using the git protocol for fetching. If the variable value is
+	in the "COMMAND for DOMAIN" format, the command is applied only
+	on hostnames ending with the specified domain string. This variable
+	may be set multiple times and is matched in the given order;
+	the first match wins.
+
+	Can be overriden by the 'GIT_PROXY_COMMAND' environment variable
+	(which always applies universally, without the special "for"
+	handling).
+
+core.ignoreStat::
+	The working copy files are assumed to stay unchanged until you
+	mark them otherwise manually - Git will not detect the file changes
+	by lstat() calls. This is useful on systems where those are very
+	slow, such as Microsoft Windows.  See gitlink:git-update-index[1].
+	False by default.
+
+core.onlyUseSymrefs::
+	Always use the "symref" format instead of symbolic links for HEAD
+	and other symbolic reference files. True by default.
+
+core.repositoryFormatVersion::
+	Internal variable identifying the repository format and layout
+	version.
+
+core.sharedRepository::
+	If true, the repository is made shareable between several users
+	in a group (making sure all the files and objects are group-writable).
+	See gitlink:git-init-db[1]. False by default.
+
+core.warnAmbiguousRefs::
+	If true, git will warn you if the ref name you passed it is ambiguous
+	and might match multiple refs in the .git/refs/ tree. True by default.
+
+apply.whitespace::
+	Tells `git-apply` how to handle whitespaces, in the same way
+	as the '--whitespace' option. See gitlink:git-apply[1].
+
+diff.renameLimit::
+	The number of files to consider when performing the copy/rename
+	detection; equivalent to the git diff option '-l'.
+
+format.headers::
+	Additional email headers to include in a patch to be submitted
+	by mail.  See gitlink:git-format-patch[1].
+
+gitcvs.enabled::
+	Whether the cvs pserver interface is enabled for this repository.
+	See gitlink:git-cvsserver[1].
+
+gitcvs.logfile::
+	Path to a log file where the cvs pserver interface well... logs
+	various stuff. See gitlink:git-cvsserver[1].
+
+http.sslVerify::
+	Whether to verify the SSL certificate when fetching or pushing
+	over HTTPS. Can be overriden by the 'GIT_SSL_NO_VERIFY' environment
+	variable.
+
+http.sslCert::
+	File containing the SSL certificate when fetching or pushing
+	over HTTPS. Can be overriden by the 'GIT_SSL_CERT' environment
+	variable.
+
+http.sslKey::
+	File containing the SSL private key when fetching or pushing
+	over HTTPS. Can be overriden by the 'GIT_SSL_KEY' environment
+	variable.
+
+http.sslCAInfo::
+	File containing the certificates to verify the peer with when
+	fetching or pushing over HTTPS. Can be overriden by the
+	'GIT_SSL_CAINFO' environment variable.
+
+http.sslCAPath::
+	Path containing files with the CA certificates to verify the peer
+	with when fetching or pushing over HTTPS. Can be overriden
+	by the 'GIT_SSL_CAPATH' environment variable.
+
+http.maxRequests::
+	How many HTTP requests to launch in parallel. Can be overriden
+	by the 'GIT_HTTP_MAX_REQUESTS' environment variable. Default is 5.
+
+http.lowSpeedLimit, http.lowSpeedTime::
+	If the HTTP transfer speed is less than 'http.lowSpeedLimit'
+	for longer than 'http.lowSpeedTime' seconds, the transfer is aborted.
+	Can be overriden by the 'GIT_HTTP_LOW_SPEED_LIMIT' and
+	'GIT_HTTP_LOW_SPEED_TIME' environment variables.
+
+i18n.commitEncoding::
+	Character encoding the commit messages are stored in; git itself
+	does not care per se, but this information is necessary e.g. when
+	importing commits from emails or in the gitk graphical history
+	browser (and possibly at other places in the future or in other
+	porcelains). See e.g. gitlink:git-mailinfo[1]. Defaults to 'utf-8'.
+
+merge.summary::
+	Whether to include summaries of merged commits in newly created
+	merge commit messages. False by default.
+
+pull.octopus::
+	The default merge strategy to use when pulling multiple branches
+	at once.
+
+pull.twohead::
+	The default merge strategy to use when pulling a single branch.
+
+show.difftree::
+	The default gitlink:git-diff-tree[1] arguments to be used
+	for gitlink:git-show[1].
+
+showbranch.default::
+	The default set of branches for gitlink:git-show-branch[1].
+	See gitlink:git-show-branch[1].
+
+user.email::
+	Your email address to be recorded in any newly created commits.
+	Can be overriden by the 'GIT_AUTHOR_EMAIL' and 'GIT_COMMITTER_EMAIL'
+	environment variables.  See gitlink:git-commit-tree[1].
+
+user.name::
+	Your full name to be recorded in any newly created commits.
+	Can be overriden by the 'GIT_AUTHOR_NAME' and 'GIT_COMMITTER_NAME'
+	environment variables.  See gitlink:git-commit-tree[1].
+
+whatchanged.difftree::
+	The default gitlink:git-diff-tree[1] arguments to be used
+	for gitlink:git-whatchanged[1].
+
+imap::
+	The configuration variables in the 'imap' section are described
+	in gitlink:git-imap-send[1].
diff --git a/Documentation/git-repo-config.txt b/Documentation/git-repo-config.txt
index 26759a8071..71f96bdd10 100644
--- a/Documentation/git-repo-config.txt
+++ b/Documentation/git-repo-config.txt
@@ -87,11 +87,11 @@ Given a .git/config like this:
 		renames = true
 
 	; Proxy settings
-	[proxy]
-		command="ssh" for "ssh://kernel.org/"
-		command="proxy-command" for kernel.org
-		command="myprotocol-command" for "my://"
-		command=default-proxy ; for all the rest
+	[core]
+		gitproxy="ssh" for "ssh://kernel.org/"
+		gitproxy="proxy-command" for kernel.org
+		gitproxy="myprotocol-command" for "my://"
+		gitproxy=default-proxy ; for all the rest
 
 you can set the filemode to true with
 
@@ -104,7 +104,7 @@ to what URL they apply. Here is how to change the entry for kernel.org
 to "ssh".
 
 ------------
-% git repo-config proxy.command '"ssh" for kernel.org' 'for kernel.org$'
+% git repo-config core.gitproxy '"ssh" for kernel.org' 'for kernel.org$'
 ------------
 
 This makes sure that only the key/value pair for kernel.org is replaced.
@@ -115,7 +115,7 @@ To delete the entry for renames, do
 % git repo-config --unset diff.renames
 ------------
 
-If you want to delete an entry for a multivar (like proxy.command above),
+If you want to delete an entry for a multivar (like core.gitproxy above),
 you have to provide a regex matching the value of exactly one line.
 
 To query the value for a given key, do
@@ -133,27 +133,27 @@ or
 or, to query a multivar:
 
 ------------
-% git repo-config --get proxy.command "for kernel.org$"
+% git repo-config --get core.gitproxy "for kernel.org$"
 ------------
 
 If you want to know all the values for a multivar, do:
 
 ------------
-% git repo-config --get-all proxy.command
+% git repo-config --get-all core.gitproxy
 ------------
 
-If you like to live dangerous, you can replace *all* proxy.commands by a
+If you like to live dangerous, you can replace *all* core.gitproxy by a
 new one with
 
 ------------
-% git repo-config --replace-all proxy.command ssh
+% git repo-config --replace-all core.gitproxy ssh
 ------------
 
 However, if you really only want to replace the line for the default proxy,
 i.e. the one without a "for ..." postfix, do something like this:
 
 ------------
-% git repo-config proxy.command ssh '! for '
+% git repo-config core.gitproxy ssh '! for '
 ------------
 
 To actually match only values with an exclamation mark, you have to
@@ -163,13 +163,16 @@ To actually match only values with an exclamation mark, you have to
 ------------
 
 
+include::config.txt[]
+
+
 Author
 ------
 Written by Johannes Schindelin <Johannes.Schindelin@gmx.de>
 
 Documentation
 --------------
-Documentation by Johannes Schindelin.
+Documentation by Johannes Schindelin, Petr Baudis and the git-list <git@vger.kernel.org>.
 
 GIT
 ---
diff --git a/Documentation/git-var.txt b/Documentation/git-var.txt
index 90cb157be5..379571eef0 100644
--- a/Documentation/git-var.txt
+++ b/Documentation/git-var.txt
@@ -17,7 +17,9 @@ Prints a git logical variable.
 OPTIONS
 -------
 -l::
-	Cause the logical variables to be listed.
+	Cause the logical variables to be listed. In addition, all the
+	variables of the git configuration file .git/config are listed
+	as well.
 
 EXAMPLE
 --------
@@ -46,6 +48,7 @@ See Also
 --------
 gitlink:git-commit-tree[1]
 gitlink:git-tag[1]
+gitlink:git-repo-config[1]
 
 Author
 ------
diff --git a/config.c b/config.c
index 7ea8a7369a..4e1f0c2286 100644
--- a/config.c
+++ b/config.c
@@ -252,7 +252,7 @@ int git_default_config(const char *var, const char *value)
 		return 0;
 	}
 
-	/* Add other config variables here.. */
+	/* Add other config variables here and to Documentation/config.txt. */
 	return 0;
 }
 
diff --git a/delta.h b/delta.h
index 9464f3e9b0..727ae30e9e 100644
--- a/delta.h
+++ b/delta.h
@@ -1,12 +1,73 @@
 #ifndef DELTA_H
 #define DELTA_H
 
-/* handling of delta buffers */
-extern void *diff_delta(void *from_buf, unsigned long from_size,
-			void *to_buf, unsigned long to_size,
-		        unsigned long *delta_size, unsigned long max_size);
-extern void *patch_delta(void *src_buf, unsigned long src_size,
-			 void *delta_buf, unsigned long delta_size,
+/* opaque object for delta index */
+struct delta_index;
+
+/*
+ * create_delta_index: compute index data from given buffer
+ *
+ * This returns a pointer to a struct delta_index that should be passed to
+ * subsequent create_delta() calls, or to free_delta_index().  A NULL pointer
+ * is returned on failure.  The given buffer must not be freed nor altered
+ * before free_delta_index() is called.  The returned pointer must be freed
+ * using free_delta_index().
+ */
+extern struct delta_index *
+create_delta_index(const void *buf, unsigned long bufsize);
+
+/*
+ * free_delta_index: free the index created by create_delta_index()
+ */
+extern void free_delta_index(struct delta_index *index);
+
+/*
+ * create_delta: create a delta from given index for the given buffer
+ *
+ * This function may be called multiple times with different buffers using
+ * the same delta_index pointer.  If max_delta_size is non-zero and the
+ * resulting delta is to be larger than max_delta_size then NULL is returned.
+ * On success, a non-NULL pointer to the buffer with the delta data is
+ * returned and *delta_size is updated with its size.  The returned buffer
+ * must be freed by the caller.
+ */
+extern void *
+create_delta(const struct delta_index *index,
+	     const void *buf, unsigned long bufsize,
+	     unsigned long *delta_size, unsigned long max_delta_size);
+
+/*
+ * diff_delta: create a delta from source buffer to target buffer
+ *
+ * If max_delta_size is non-zero and the resulting delta is to be larger
+ * than max_delta_size then NULL is returned.  On success, a non-NULL
+ * pointer to the buffer with the delta data is returned and *delta_size is
+ * updated with its size.  The returned buffer must be freed by the caller.
+ */
+static inline void *
+diff_delta(const void *src_buf, unsigned long src_bufsize,
+	   const void *trg_buf, unsigned long trg_bufsize,
+	   unsigned long *delta_size, unsigned long max_delta_size)
+{
+	struct delta_index *index = create_delta_index(src_buf, src_bufsize);
+	if (index) {
+		void *delta = create_delta(index, trg_buf, trg_bufsize,
+					   delta_size, max_delta_size);
+		free_delta_index(index);
+		return delta;
+	}
+	return NULL;
+}
+
+/*
+ * patch_delta: recreate target buffer given source buffer and delta data
+ *
+ * On success, a non-NULL pointer to the target buffer is returned and
+ * *trg_bufsize is updated with its size.  On failure a NULL pointer is
+ * returned.  The returned buffer must be freed by the caller.
+ */
+extern void *patch_delta(const void *src_buf, unsigned long src_size,
+			 const void *delta_buf, unsigned long delta_size,
 			 unsigned long *dst_size);
 
 /* the smallest possible delta size is 4 bytes */
@@ -14,7 +75,7 @@ extern void *patch_delta(void *src_buf, unsigned long src_size,
 
 /*
  * This must be called twice on the delta data buffer, first to get the
- * expected reference buffer size, and again to get the result buffer size.
+ * expected source buffer size, and again to get the target buffer size.
  */
 static inline unsigned long get_delta_hdr_size(const unsigned char **datap,
 					       const unsigned char *top)
diff --git a/diff-delta.c b/diff-delta.c
index 1188b31cd0..fdedf94cce 100644
--- a/diff-delta.c
+++ b/diff-delta.c
@@ -27,53 +27,70 @@
 /* block size: min = 16, max = 64k, power of 2 */
 #define BLK_SIZE 16
 
-#define MIN(a, b) ((a) < (b) ? (a) : (b))
+/* maximum hash entry list for the same hash bucket */
+#define HASH_LIMIT 64
 
 #define GR_PRIME 0x9e370001
 #define HASH(v, shift) (((unsigned int)(v) * GR_PRIME) >> (shift))
 
-struct index {
+struct index_entry {
 	const unsigned char *ptr;
 	unsigned int val;
-	struct index *next;
+	struct index_entry *next;
 };
 
-static struct index ** delta_index(const unsigned char *buf,
-				   unsigned long bufsize,
-				   unsigned long trg_bufsize,
-				   unsigned int *hash_shift)
+struct delta_index {
+	const void *src_buf;
+	unsigned long src_size;
+	unsigned int hash_shift;
+	struct index_entry *hash[0];
+};
+
+struct delta_index * create_delta_index(const void *buf, unsigned long bufsize)
 {
-	unsigned int i, hsize, hshift, hlimit, entries, *hash_count;
-	const unsigned char *data;
-	struct index *entry, **hash;
+	unsigned int i, hsize, hshift, entries, *hash_count;
+	const unsigned char *data, *buffer = buf;
+	struct delta_index *index;
+	struct index_entry *entry, **hash;
 	void *mem;
 
+	if (!buf || !bufsize)
+		return NULL;
+
 	/* determine index hash size */
 	entries = bufsize  / BLK_SIZE;
 	hsize = entries / 4;
 	for (i = 4; (1 << i) < hsize && i < 31; i++);
 	hsize = 1 << i;
 	hshift = 32 - i;
-	*hash_shift = hshift;
 
 	/* allocate lookup index */
-	mem = malloc(hsize * sizeof(*hash) + entries * sizeof(*entry));
+	mem = malloc(sizeof(*index) +
+		     sizeof(*hash) * hsize +
+		     sizeof(*entry) * entries);
 	if (!mem)
 		return NULL;
+	index = mem;
+	mem = index + 1;
 	hash = mem;
-	entry = mem + hsize * sizeof(*hash);
+	mem = hash + hsize;
+	entry = mem;
+
+	index->src_buf = buf;
+	index->src_size = bufsize;
+	index->hash_shift = hshift;
 	memset(hash, 0, hsize * sizeof(*hash));
 
 	/* allocate an array to count hash entries */
 	hash_count = calloc(hsize, sizeof(*hash_count));
 	if (!hash_count) {
-		free(hash);
+		free(index);
 		return NULL;
 	}
 
 	/* then populate the index */
-	data = buf + entries * BLK_SIZE - BLK_SIZE;
-	while (data >= buf) {
+	data = buffer + entries * BLK_SIZE - BLK_SIZE;
+	while (data >= buffer) {
 		unsigned int val = adler32(0, data, BLK_SIZE);
 		i = HASH(val, hshift);
 		entry->ptr = data;
@@ -91,27 +108,18 @@ static struct index ** delta_index(const unsigned char *buf,
 	 * bucket that would bring us to O(m*n) computing costs (m and n
 	 * corresponding to reference and target buffer sizes).
 	 *
-	 * The more the target buffer is large, the more it is important to
-	 * have small entry lists for each hash buckets.  With such a limit
-	 * the cost is bounded to something more like O(m+n).
-	 */
-	hlimit = (1 << 26) / trg_bufsize;
-	if (hlimit < 4*BLK_SIZE)
-		hlimit = 4*BLK_SIZE;
-
-	/*
-	 * Now make sure none of the hash buckets has more entries than
+	 * Make sure none of the hash buckets has more entries than
 	 * we're willing to test.  Otherwise we cull the entry list
 	 * uniformly to still preserve a good repartition across
 	 * the reference buffer.
 	 */
 	for (i = 0; i < hsize; i++) {
-		if (hash_count[i] < hlimit)
+		if (hash_count[i] < HASH_LIMIT)
 			continue;
 		entry = hash[i];
 		do {
-			struct index *keep = entry;
-			int skip = hash_count[i] / hlimit / 2;
+			struct index_entry *keep = entry;
+			int skip = hash_count[i] / HASH_LIMIT / 2;
 			do {
 				entry = entry->next;
 			} while(--skip && entry);
@@ -120,7 +128,12 @@ static struct index ** delta_index(const unsigned char *buf,
 	}
 	free(hash_count);
 
-	return hash;
+	return index;
+}
+
+void free_delta_index(struct delta_index *index)
+{
+	free(index);
 }
 
 /* provide the size of the copy opcode given the block offset and size */
@@ -131,21 +144,17 @@ static struct index ** delta_index(const unsigned char *buf,
 /* the maximum size for any opcode */
 #define MAX_OP_SIZE COPYOP_SIZE(0xffffffff, 0xffffffff)
 
-void *diff_delta(void *from_buf, unsigned long from_size,
-		 void *to_buf, unsigned long to_size,
-		 unsigned long *delta_size,
-		 unsigned long max_size)
+void *
+create_delta(const struct delta_index *index,
+	     const void *trg_buf, unsigned long trg_size,
+	     unsigned long *delta_size, unsigned long max_size)
 {
 	unsigned int i, outpos, outsize, hash_shift;
 	int inscnt;
 	const unsigned char *ref_data, *ref_top, *data, *top;
 	unsigned char *out;
-	struct index *entry, **hash;
 
-	if (!from_size || !to_size)
-		return NULL;
-	hash = delta_index(from_buf, from_size, to_size, &hash_shift);
-	if (!hash)
+	if (!trg_buf || !trg_size)
 		return NULL;
 
 	outpos = 0;
@@ -153,60 +162,55 @@ void *diff_delta(void *from_buf, unsigned long from_size,
 	if (max_size && outsize >= max_size)
 		outsize = max_size + MAX_OP_SIZE + 1;
 	out = malloc(outsize);
-	if (!out) {
-		free(hash);
+	if (!out)
 		return NULL;
-	}
-
-	ref_data = from_buf;
-	ref_top = from_buf + from_size;
-	data = to_buf;
-	top = to_buf + to_size;
 
 	/* store reference buffer size */
-	out[outpos++] = from_size;
-	from_size >>= 7;
-	while (from_size) {
-		out[outpos - 1] |= 0x80;
-		out[outpos++] = from_size;
-		from_size >>= 7;
+	i = index->src_size;
+	while (i >= 0x80) {
+		out[outpos++] = i | 0x80;
+		i >>= 7;
 	}
+	out[outpos++] = i;
 
 	/* store target buffer size */
-	out[outpos++] = to_size;
-	to_size >>= 7;
-	while (to_size) {
-		out[outpos - 1] |= 0x80;
-		out[outpos++] = to_size;
-		to_size >>= 7;
+	i = trg_size;
+	while (i >= 0x80) {
+		out[outpos++] = i | 0x80;
+		i >>= 7;
 	}
+	out[outpos++] = i;
 
+	ref_data = index->src_buf;
+	ref_top = ref_data + index->src_size;
+	data = trg_buf;
+	top = trg_buf + trg_size;
+	hash_shift = index->hash_shift;
 	inscnt = 0;
 
 	while (data < top) {
 		unsigned int moff = 0, msize = 0;
-		if (data + BLK_SIZE <= top) {
-			unsigned int val = adler32(0, data, BLK_SIZE);
-			i = HASH(val, hash_shift);
-			for (entry = hash[i]; entry; entry = entry->next) {
-				const unsigned char *ref = entry->ptr;
-				const unsigned char *src = data;
-				unsigned int ref_size = ref_top - ref;
-				if (entry->val != val)
-					continue;
-				if (ref_size > top - src)
-					ref_size = top - src;
-				if (ref_size > 0x10000)
-					ref_size = 0x10000;
-				if (ref_size <= msize)
-					break;
-				while (ref_size-- && *src++ == *ref)
-					ref++;
-				if (msize < ref - entry->ptr) {
-					/* this is our best match so far */
-					msize = ref - entry->ptr;
-					moff = entry->ptr - ref_data;
-				}
+		struct index_entry *entry;
+		unsigned int val = adler32(0, data, BLK_SIZE);
+		i = HASH(val, hash_shift);
+		for (entry = index->hash[i]; entry; entry = entry->next) {
+			const unsigned char *ref = entry->ptr;
+			const unsigned char *src = data;
+			unsigned int ref_size = ref_top - ref;
+			if (entry->val != val)
+				continue;
+			if (ref_size > top - src)
+				ref_size = top - src;
+			if (ref_size > 0x10000)
+				ref_size = 0x10000;
+			if (ref_size <= msize)
+				break;
+			while (ref_size-- && *src++ == *ref)
+				ref++;
+			if (msize < ref - entry->ptr) {
+				/* this is our best match so far */
+				msize = ref - entry->ptr;
+				moff = entry->ptr - ref_data;
 			}
 		}
 
@@ -271,7 +275,6 @@ void *diff_delta(void *from_buf, unsigned long from_size,
 				out = realloc(out, outsize);
 			if (!out) {
 				free(tmp);
-				free(hash);
 				return NULL;
 			}
 		}
@@ -280,7 +283,6 @@ void *diff_delta(void *from_buf, unsigned long from_size,
 	if (inscnt)
 		out[outpos - inscnt - 1] = inscnt;
 
-	free(hash);
 	*delta_size = outpos;
 	return out;
 }
diff --git a/patch-delta.c b/patch-delta.c
index d95f0d9721..8f318ed8aa 100644
--- a/patch-delta.c
+++ b/patch-delta.c
@@ -13,8 +13,8 @@
 #include <string.h>
 #include "delta.h"
 
-void *patch_delta(void *src_buf, unsigned long src_size,
-		  void *delta_buf, unsigned long delta_size,
+void *patch_delta(const void *src_buf, unsigned long src_size,
+		  const void *delta_buf, unsigned long delta_size,
 		  unsigned long *dst_size)
 {
 	const unsigned char *data, *top;
diff --git a/rev-parse.c b/rev-parse.c
index e956cd5ed5..7f66ae2db8 100644
--- a/rev-parse.c
+++ b/rev-parse.c
@@ -160,6 +160,14 @@ static int show_file(const char *arg)
 	return 0;
 }
 
+static void die_badfile(const char *arg)
+{
+	if (errno != ENOENT)
+		die("'%s': %s", arg, strerror(errno));
+	die("'%s' is ambiguous - revision name or file/directory name?\n"
+	    "Please put '--' before the list of filenames.", arg);
+}
+
 int main(int argc, char **argv)
 {
 	int i, as_is = 0, verify = 0;
@@ -176,7 +184,7 @@ int main(int argc, char **argv)
 		if (as_is) {
 			if (show_file(arg) && as_is < 2)
 				if (lstat(arg, &st) < 0)
-					die("'%s': %s", arg, strerror(errno));
+					die_badfile(arg);
 			continue;
 		}
 		if (!strcmp(arg,"-n")) {
@@ -343,7 +351,7 @@ int main(int argc, char **argv)
 		if (verify)
 			die("Needed a single revision");
 		if (lstat(arg, &st) < 0)
-			die("'%s': %s", arg, strerror(errno));
+			die_badfile(arg);
 	}
 	show_default();
 	if (verify && revs_count != 1)