On Mon, 28 Mar 2011, Gianni Tedesco wrote:
> On Thu, 2011-03-24 at 17:49 +0000, Ian Jackson wrote:
> > From: Ian Jackson <ijackson@xxxxxxxxxxxxxxxxxxxxxx>
> >
> > Introduce new flex/regexp-based parser for disk configuration strings.
> >
> > Callers will be updated in following patches.
> >
> > Signed-off-by: Ian Jackson <ijackson@xxxxxxxxxxxxxxxxxxxxxx>
> > ---
> > config/StdGNU.mk | 1 +
> > tools/libxl/Makefile | 9 +-
> > tools/libxl/libxlu_cfg.c | 42 +++++++---
> > tools/libxl/libxlu_disk.c | 164
> > +++++++++++++++++++++++++++++++++++++++++
> > tools/libxl/libxlu_disk_i.h | 19 +++++
> > tools/libxl/libxlu_disk_l.l | 54 ++++++++++++++
> > tools/libxl/libxlu_internal.h | 20 +++++
> > tools/libxl/libxlutil.h | 12 +++
> > 8 files changed, 304 insertions(+), 17 deletions(-)
> > create mode 100644 tools/libxl/libxlu_disk.c
> > create mode 100644 tools/libxl/libxlu_disk_i.h
> > create mode 100644 tools/libxl/libxlu_disk_l.l
> >
> > diff --git a/config/StdGNU.mk b/config/StdGNU.mk
> > index 25aeb4d..9b331f0 100644
> > --- a/config/StdGNU.mk
> > +++ b/config/StdGNU.mk
> > @@ -67,6 +67,7 @@ CURSES_LIBS = -lncurses
> > PTHREAD_LIBS = -lpthread
> > UTIL_LIBS = -lutil
> > DLOPEN_LIBS = -ldl
> > +PCRE_LIBS = -lpcre
> >
> > SONAME_LDFLAG = -soname
> > SHLIB_LDFLAGS = -shared
> > diff --git a/tools/libxl/Makefile b/tools/libxl/Makefile
> > index a7b1d51..f0c473f 100644
> > --- a/tools/libxl/Makefile
> > +++ b/tools/libxl/Makefile
> > @@ -22,7 +22,7 @@ endif
> > LIBXL_LIBS =
> > LIBXL_LIBS = $(LDLIBS_libxenctrl) $(LDLIBS_libxenguest)
> > $(LDLIBS_libxenstore) $(LDLIBS_libblktapctl) $(UTIL_LIBS) $(LIBUUID_LIBS)
> >
> > -LIBXLU_LIBS =
> > +LIBXLU_LIBS = $(PCRE_LIBS)
> >
> > LIBXL_OBJS-y = osdeps.o libxl_paths.o libxl_bootloader.o flexarray.o
> > ifeq ($(LIBXL_BLKTAP),y)
> > @@ -38,9 +38,10 @@ LIBXL_OBJS = flexarray.o libxl.o libxl_create.o
> > libxl_dm.o libxl_pci.o \
> > libxl_internal.o libxl_utils.o $(LIBXL_OBJS-y)
> > LIBXL_OBJS += _libxl_types.o
> >
> > -AUTOINCS= libxlu_cfg_y.h libxlu_cfg_l.h
> > -AUTOSRCS= libxlu_cfg_y.c libxlu_cfg_l.c
> > -LIBXLU_OBJS = libxlu_cfg_y.o libxlu_cfg_l.o libxlu_cfg.o
> > +AUTOINCS= libxlu_cfg_y.h libxlu_cfg_l.h libxlu_disk_l.h
> > +AUTOSRCS= libxlu_cfg_y.c libxlu_cfg_l.c libxlu_disk_l.c
> > +LIBXLU_OBJS = libxlu_cfg_y.o libxlu_cfg_l.o libxlu_cfg.o \
> > + libxlu_disk_l.o libxlu_disk.o
> >
> > CLIENTS = xl
> >
> > diff --git a/tools/libxl/libxlu_cfg.c b/tools/libxl/libxlu_cfg.c
> > index f947c21..fd3e102 100644
> > --- a/tools/libxl/libxlu_cfg.c
> > +++ b/tools/libxl/libxlu_cfg.c
> > @@ -15,6 +15,7 @@ XLU_Config *xlu_cfg_init(FILE *report, const char
> > *report_filename) {
> > if (!cfg->filename) { free(cfg); return 0; }
> >
> > cfg->settings= 0;
> > + cfg->disk_re= 0;
> > return cfg;
> > }
> >
> > @@ -38,6 +39,29 @@ static int ctx_prep(CfgParseContext *ctx, XLU_Config
> > *cfg) {
> >
> > static void ctx_dispose(CfgParseContext *ctx) {
> > if (ctx->scanner) xlu__cfg_yylex_destroy(ctx->scanner);
> > + if (ctx->disk_re) pcre_free(ctx->disk_re);
> > +}
> > +
> > +int xlu__scanner_string_prep(CfgParseContext *ctx, YY_BUFFER_STATE *buf,
> > + XLU_Config *cfg, const char *data, int length)
> > {
> > + int e;
> > +
> > + e= ctx_prep(ctx, cfg);
> > + if (e) return e;
> > +
> > + *buf = xlu__cfg_yy_scan_bytes(data, length, ctx->scanner);
> > + if (!*buf) {
> > + fprintf(cfg->report,"%s: unable to allocate scanner buffer\n",
> > + cfg->filename);
> > + return ENOMEM;
> > + }
> > +
> > + return 0;
> > +}
> > +
> > +void xlu__scanner_string_dispose(CfgParseContext *ctx, YY_BUFFER_STATE
> > *buf) {
> > + if (*buf) xlu__cfg_yy_delete_buffer(*buf, ctx->scanner);
> > + ctx_dispose(ctx);
> > }
> >
> > static void parse(CfgParseContext *ctx) {
> > @@ -87,25 +111,17 @@ int xlu_cfg_readfile(XLU_Config *cfg, const char
> > *real_filename) {
> >
> > int xlu_cfg_readdata(XLU_Config *cfg, const char *data, int length) {
> > int e;
> > - YY_BUFFER_STATE buf= 0;
> > -
> > + YY_BUFFER_STATE buf=0;
> > CfgParseContext ctx;
> > - e= ctx_prep(&ctx, cfg);
> > - if (e) { ctx.err= e; goto xe; }
> > + ctx.scanner=0;
> >
> > - buf = xlu__cfg_yy_scan_bytes(data, length, ctx.scanner);
> > - if (!buf) {
> > - fprintf(cfg->report,"%s: unable to allocate scanner buffer\n",
> > - cfg->filename);
> > - ctx.err= ENOMEM;
> > - goto xe;
> > - }
> > + e = xlu__scanner_string_prep(&ctx,&buf, cfg,data,length);
> > + if (e) { ctx.err = e; goto xe; }
> >
> > parse(&ctx);
> >
> > xe:
> > - if (buf) xlu__cfg_yy_delete_buffer(buf, ctx.scanner);
> > - ctx_dispose(&ctx);
> > + xlu__scanner_string_dispose(&ctx,&buf);
> >
> > return ctx.err;
> > }
> > diff --git a/tools/libxl/libxlu_disk.c b/tools/libxl/libxlu_disk.c
> > new file mode 100644
> > index 0000000..be523f7
> > --- /dev/null
> > +++ b/tools/libxl/libxlu_disk.c
> > @@ -0,0 +1,164 @@
> > +
> > +/* Parsing the disk spec a tricky problem, because the target
> > + * string might contain "," which is the delimiter we use for
> > + * stripping off things on the RHS, and ":", which is the delimiter
> > + * we use for stripping off things on the LHS.
> > + *
> > + * For the LHS we use a flex scanner, see libxlu_disk_l.l.
> > + * That chops prefixes like "phy:" from the front of the string,
> > + * accumulating information into the disk structure.
> > + *
> > + * For the RHS, we use a regexp using pcre.
> > + */
> > +
> > +#include "libxlu_internal.h"
> > +#include "libxlu_disk_l.h"
> > +#include "libxlu_disk_i.h"
> > +#include "libxlu_cfg_i.h"
> > +
> > +static void err_core(DiskParseContext *dpc, const char *message,
> > + const char *in, int inlen) {
> > + fprintf(dpc->ctx.cfg->report,
> > + "%s: config parsing error in disk specification:"
> > + " %s: near `%s' in `%.*s'\n",
> > + dpc->ctx.cfg->filename, message, dpc->spec, inlen, in);
> > + if (!dpc->ctx.err) dpc->ctx.err= EINVAL;
> > +}
> > +
> > +void xlu__disk_err(DiskParseContext *dpc, const char *message) {
> > + err_core(dpc, message,
> > + xlu__disk_yyget_text(dpc->ctx.scanner),
> > + xlu__disk_yyget_leng(dpc->ctx.scanner));
> > +}
> > +
> > +void xlu__disk_rhs(DiskParseContext *dpc) {
> > +
> > + /* variables used by pcre */
> > +#define WORKSPACE_SIZE 20 /* wtf no manifest constant from pcre */
> > +#define OVECTOR_SIZE 10
> > + int ovector[OVECTOR_SIZE];
> > + int workspace[WORKSPACE_SIZE];
> > +
> > + int rc, len;
> > + const char *text;
> > + libxl_device_disk *disk = dpc->disk;
> > +
> > + static const char *re_text=
> > + "(.*),(?:/dev/)?([0-9a-zA-Z]*)(:[0-9a-z]+)?(,[0-9a-z]*)?"
> > + /* 1:target 2:vdev 3:type 4:attrib (r/w) */;
> > +
> > + /* compile the regexp if we haven't got one already */
> > + if (!dpc->ctx.disk_re) {
> > + const char *re_errstr;
> > + int re_errcode, re_erroffset;
> > +
> > + dpc->ctx.disk_re = pcre_compile2(re_text, PCRE_DOTALL,
> > + &re_errcode, &re_errstr,
> > &re_erroffset,
> > + 0);
> > + if (!dpc->ctx.disk_re) {
> > + if (re_errcode == 21 /* wtf, no manifest constant */) {
> > + dpc->ctx.err = ENOMEM;
> > + return;
> > + }
> > + fprintf(dpc->ctx.cfg->report, "config parsing:"
> > + " unable to compile regexp: %s [%d] (at `%s')",
> > + re_errstr, re_errcode, re_text+re_erroffset);
> > + dpc->ctx.err = EIO;
> > + return;
> > + }
> > + }
> > +
> > + /* actually run the regexp match */
> > +
> > + text = xlu__disk_yyget_text(dpc->ctx.scanner);
> > + len = xlu__disk_yyget_leng(dpc->ctx.scanner);
> > +
> > + rc = pcre_dfa_exec(dpc->ctx.disk_re, 0,
> > + text, len, 0,
> > + PCRE_ANCHORED,
> > + ovector, OVECTOR_SIZE,
> > + workspace, WORKSPACE_SIZE);
> > + switch (rc) {
> > + case PCRE_ERROR_NOMATCH:
> > + xlu__disk_err(dpc, "bad syntax for target, or missing vdev");
> > + return;
>
> case 1: ??
>
> > + case 2:
> > + case 3:
> > + case 4:
> > + break;
>
> Or does it belong here? In which case aborting on a parse error is bad
> juju.
> case 1:
>
> > + default:
> > + abort();
> > + }
> > +
> > + /* macros for processing info from capturing parens; see pcreapi(3) */
> > +
> > +#define CAPTURED(cap) (START((cap)) >= 0)
> > +#define START(cap) (ovector[(cap)*2])
> > +#define END(cap) (ovector[(cap)*2+1])
> > +#define LEN(cap) (END((cap)) - START((cap)))
> > +#define TEXT(cap) (text + START((cap)))
> > +
> > +#define STORE(cap, member) do{ \
> > + assert(CAPTURED((cap))); \
> > + free(disk->member); \
> > + disk->member = malloc(LEN((cap)) + 1); \
> > + if (!disk->member) { dpc->ctx.err = ENOMEM; return; } \
> > + memcpy(disk->member, TEXT((cap)), LEN((cap))); \
> > + disk->member[LEN((cap))] = 0; \
> > +}while(0)
> > +
> > +#define EXACTLY(cap, string) \
> > + (CAPTURED((cap)) && \
> > + LEN((cap))==strlen((string)) && \
> > + !memcmp(TEXT((cap)), (string), LEN((cap))))
> > +
> > +#define ERR(cap, msg) \
> > + err_core(dpc, (msg), TEXT((cap)), LEN((cap)))
> > +
> > + /* actually process the four capturing parens in our regexp */
> > +
> > + STORE(1, pdev_path);
> > +
> > + STORE(2, vdev);
> > +
> > + if (!CAPTURED(3) || EXACTLY(3, ":")) {
> > + disk->is_cdrom = 0;
> > + } else if (EXACTLY(3, ":cdrom")) {
> > + disk->is_cdrom = 1;
> > + } else {
> > + ERR(3, "unknown type (only `:' and `:cdrom' supported)");
> > + }
> > +
> > + if (!CAPTURED(4) || EXACTLY(4, ",w") || EXACTLY(4, ",")) {
> > + disk->readwrite = 1;
> > + } else if (EXACTLY(4, ",r")) {
> > + disk->readwrite = 0;
> > + } else {
> > + ERR(4, "unknown read/write attribute");
> > + }
> > +}
>
> Hmm, I'm not sure this is nicer than the code it's replacing, it's
> certainly a lot longer. I don't like the idea of it being full of things
> comparing for ",w" or ":cdrom" etc, rather than tokenising it fully and
> evaluating what the tokens are separately.
I definitely agree.
Besides when doing refactoring the code produced should be either shorter or
at least easier to read but this code is neither of them.
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