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patch: apply patches atomically

When applying a patch, we used to write out the patch,
rename the file, and then move to the next one. This
meant that if a patch failed to apply cleanly, we would
leave the patch half-applied.

This sucked, so we now apply the patch as a whole unit,
or not at all.

--- a/sys/src/cmd/patch.c

+++ b/sys/src/cmd/patch.c

@@ -6,6 +6,7 @@

 typedef struct Patch Patch;

 typedef struct Hunk Hunk;

 typedef struct Fbuf Fbuf;

+typedef struct Fchg Fchg;

 struct Patch {

 	char	*name;

@@ -39,10 +40,18 @@

 	int	len;

 };

+struct Fchg {

+	char	*tmp;

+	char	*old;

+	char	*new;

+};

+

 int	strip;

 int	reverse;

 void	(*addnew)(Hunk*, char*);

 void	(*addold)(Hunk*, char*);

+Fchg	*changed;

+int	nchanged;

 char*

 readline(Biobuf *f, int *lnum)

@@ -398,15 +407,49 @@

 		sysfatal("open %s: %r", tmp);

 	if(write(fd, o, len) != len)

 		sysfatal("write %s: %r", tmp);

-	if(strcmp(old, new) == 0 && remove(old) == -1)

-		sysfatal("remove %s: %r", old);

-	if(rename(fd, new) == -1)

-		sysfatal("create %s: %r", new);

-	if(close(fd) == -1)

-		sysfatal("close %s: %r", tmp);

-	free(tmp);

+	if((changed = realloc(changed, (nchanged+1)*sizeof(Fchg))) == nil)

+		sysfatal("realloc: %r");

+	if((changed[nchanged].new = strdup(new)) == nil)

+		sysfatal("strdup: %r");

+	if((changed[nchanged].old = strdup(old)) == nil)

+		sysfatal("strdup: %r");

+	changed[nchanged].tmp = tmp;

+	nchanged++;

+	close(fd);

 }

+void

+finish(int ok)

+{

+	Fchg *c;

+	int i, fd;

+

+	for(i = 0; i < nchanged; i++){

+		c = &changed[i];

+		if(!ok){

+			if(remove(c->tmp) == -1)

+				fprint(2, "remove %s: %r\n", c->tmp);

+		}else{

+			if((fd = open(c->tmp, ORDWR)) == -1)

+				sysfatal("open %s: %r", c->tmp);

+			if(strcmp(c->old, c->new) == 0 && remove(c->old) == -1)

+				sysfatal("remove %s: %r", c->old);

+			if(rename(fd, c->new) == -1)

+				sysfatal("create %s: %r", c->new);

+			if(close(fd) == -1)

+				sysfatal("close %s: %r", c->tmp);

+			if(strcmp(c->new, "/dev/null") == 0)

+				print("%s\n", c->old);

+			else

+				print("%s\n", c->new);

+		}

+		free(c->tmp);

+		free(c->old);

+		free(c->new);

+	}

+	free(changed);

+}

+

 int

 slurp(Fbuf *f, char *path)

 {

@@ -530,10 +573,6 @@

 		if(i+1 == p->nhunk || strcmp(curfile, p->hunk[i+1].newpath) != 0){

 			o = append(o, &osz, e, f.buf + f.len);

 			blat(h->oldpath, h->newpath, o, osz);

-			if(strcmp(h->newpath, "/dev/null") == 0)

-				print("%s\n", h->oldpath);

-			else

-				print("%s\n", h->newpath);

 			osz = 0;

 		}

 	}

@@ -571,7 +610,7 @@

 {

 	Biobuf *f;

 	Patch *p;

-	int i;

+	int i, ok;

 	ARGBEGIN{

 	case 'p':

@@ -592,13 +631,16 @@

 		addnew = addnewfn;

 		addold = addoldfn;

 	}

+	ok = 1;

 	if(argc == 0){

 		if((f = Bfdopen(0, OREAD)) == nil)

 			sysfatal("open stdin: %r");

 		if((p = parse(f, "stdin")) == nil)

 			sysfatal("parse patch: %r");

-		if(apply(p, "stdin") == -1)

-			sysfatal("apply stdin: %r");

+		if(apply(p, "stdin") == -1){

+			fprint(2, "apply stdin: %r\n");

+			ok = 0;

+		}

 		freepatch(p);

 		Bterm(f);

 	}else{

@@ -607,11 +649,14 @@

 				sysfatal("open %s: %r", argv[i]);

 			if((p = parse(f, argv[i])) == nil)

 				sysfatal("parse patch: %r");

-			if(apply(p, argv[i]) == -1)

-				sysfatal("apply %s: %r", argv[i]);

+			if(apply(p, argv[i]) == -1){

+				fprint(2, "apply %s: %r\n", argv[i]);

+				ok = 0;

+			}

 			freepatch(p);

 			Bterm(f);

 		}

 	}

+	finish(ok);

 	exits(nil);

 }