update; showstopper issue with current git

developed a patch for git, we'll see if they like it..

doc/todo/smudge.mdwn

@@ -41,18 +41,17 @@ efficiently using the existing code in `Branch.catFile`.
 
 ### efficiency
 
+#### clean
+
 The trick is doing it efficiently. Since git a2b665d, v1.7.4.1,
 something like this works to provide a filename to the clean script:
 
 	git config --global filter.huge.clean huge-clean %f
 
-This avoids it needing to read all the current file content from stdin
+This could avoid it needing to read all the current file content from stdin
 when doing eg, a git status or git commit. Instead it is passed the
 filename that git is operating on, in the working directory.
 
-(The smudge script can also be provided a filename with %f, but it
-cannot directly write to the file or git gets unhappy.)
-
 So, WORM could just look at that file and easily tell if it is one
 it already knows (same mtime and size). If so, it can short-circuit and
 do nothing, file content is already cached.
@@ -61,6 +60,21 @@ SHA1 has a harder job. Would not want to re-sha1 the file every time,
 probably. So it'd need a local cache of file stat info, mapped to known
 objects.
 
+But: Even with %f, git actually passes the full file content to the clean
+filter, and if it fails to consume it all, it will crash (may only happen
+if the file is larger than some chunk size; tried with 500 mb file and 
+saw a SIGPIPE.) This means unnecessary works needs to be done, 
+and it slows down *everything*, from `git status` to `git commit`.
+**showstopper** I have sent a patch to the git mailing list to address
+this.
+
+#### smudge
+
+The smudge script can also be provided a filename with %f, but it
+cannot directly write to the file or git gets unhappy.
+
+
+
 ### dealing with partial content availability
 
 The smudge filter cannot be allowed to fail, that leaves the tree and
@@ -82,13 +96,13 @@ huge-smudge:
 
 <pre>
 #!/bin/sh
-read sha1
+read f
 file="$1"
-echo "smudging $sha1" >&2
-if [ -e ~/$sha1 ]; then
-	cat ~/$sha1 # possibly expensive copy here
+echo "smudging $f" >&2
+if [ -e ~/$f ]; then
+	cat ~/$f # possibly expensive copy here
 else
-	echo "$sha1 not available"
+	echo "$f not available"
 fi
 </pre>
 
@@ -96,16 +110,17 @@ huge-clean:
 
 <pre>
 #!/bin/sh
-temp="$1"
-if grep -q 'not available' "$temp"; then
-	awk '{print $1}' "$temp" # provide what we would if the content were avail!
+file="$1"
+# in real life, this should be done more efficiently, not trying to read
+# the whole file content!
+if grep -q 'not available' "$file"; then
+	awk '{print $1}' "$file" # provide what we would if the content were avail!
 	exit 0
 fi
-sha1=`sha1sum "$temp" | cut -d' ' -f1`
-echo "cleaning $sha1" >&2
-ls -l "$temp" >&2
-ln -f "$temp" ~/$sha1 # can't delete temp file
-echo $sha1
+echo "cleaning $file" >&2
+ls -l "$file" >&2
+ln -f "$file" ~/$file # can't delete temp file
+echo $file
 </pre>
 
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