[pacman-dev] [PATCH 2/2] Overhaul archive fgets function
Dan McGee
dan at archlinux.org
Wed Dec 15 01:48:47 EST 2010
The old function was written in a time before we relied on it for nearly
every operation. Since then, we have switched to the archive backend and now
fast parsing is a big deal.
The former function made a per-character call to the libarchive
archive_read_data() function, which resulted in some 21 million calls in a
typical "load all sync dbs" operation. If we instead do some buffering of
our own and read the blocks directly, and then find our newlines from there,
we can cut out the multiple layers of overhead and go from archive to parsed
data much quicker.
Both users of the former function are switched over to the new signature,
made easier by the macros now in place in the sync backend parsing code.
Performance: for a `pacman -Su` (no upgrades available),
_alpm_archive_fgets() goes from being 29% of the total time to 12% The time
spent on the libarchive function being called dropped from 24% to 6%.
This pushes _alpm_pkg_find back to the title of slowest low-level function.
Signed-off-by: Dan McGee <dan at archlinux.org>
---
I wish this one was a bit easier to comprehend and grok, but the cost of
performance here is a bit more complicated fgets function than the very
simplistic one we had before.
The new function revolves around the zero-copy, retrieve an entire block
functinoality of libarchive. We create a structure to keep all the bookkeeping
info we need around, including a buffer of our own where each line ends up and
auto-resizes itself as we poll through an archive file entry, and also cleans
itself up when the file is EOF. This means malloc/free is not necessary by the
caller, which keeps most concerns in the fgets function.
Please let me know if it is unclear how the new function works, so more
comments can be put in there.
-Dan
lib/libalpm/be_package.c | 12 ++++--
lib/libalpm/be_sync.c | 14 ++++--
lib/libalpm/util.c | 97 +++++++++++++++++++++++++++++++++++----------
lib/libalpm/util.h | 18 ++++++++-
4 files changed, 109 insertions(+), 32 deletions(-)
diff --git a/lib/libalpm/be_package.c b/lib/libalpm/be_package.c
index 32ec993..4c1bb08 100644
--- a/lib/libalpm/be_package.c
+++ b/lib/libalpm/be_package.c
@@ -155,17 +155,21 @@ static struct pkg_operations *get_file_pkg_ops()
*/
static int parse_descfile(struct archive *a, pmpkg_t *newpkg)
{
- char line[PATH_MAX];
char *ptr = NULL;
char *key = NULL;
int linenum = 0;
+ struct archive_read_buffer buf;
ALPM_LOG_FUNC;
- /* loop until we reach EOF (where archive_fgets will return NULL) */
- while(_alpm_archive_fgets(line, PATH_MAX, a) != NULL) {
+ memset(&buf, 0, sizeof(buf));
+ buf.max_line_size = PATH_MAX;
+
+ /* loop until we reach EOF or other error */
+ while(_alpm_archive_fgets(a, &buf) == ARCHIVE_OK) {
+ char *line = buf.line ? _alpm_strtrim(buf.line) : "";
+
linenum++;
- _alpm_strtrim(line);
if(strlen(line) == 0 || line[0] == '#') {
continue;
}
diff --git a/lib/libalpm/be_sync.c b/lib/libalpm/be_sync.c
index 137fc1b..0e688b1 100644
--- a/lib/libalpm/be_sync.c
+++ b/lib/libalpm/be_sync.c
@@ -219,8 +219,8 @@ static int sync_db_populate(pmdb_t *db)
}
#define READ_NEXT(s) do { \
- if(_alpm_archive_fgets(s, sizeof(s), archive) == NULL) goto error; \
- _alpm_strtrim(s); \
+ if(_alpm_archive_fgets(archive, &buf) != ARCHIVE_OK) goto error; \
+ s = buf.line ? _alpm_strtrim(buf.line) : ""; \
} while(0)
#define READ_AND_STORE(f) do { \
@@ -238,10 +238,10 @@ static int sync_db_populate(pmdb_t *db)
static int sync_db_read(pmdb_t *db, struct archive *archive, struct archive_entry *entry)
{
- char line[1024];
const char *entryname = NULL;
char *filename, *pkgname, *p, *q;
pmpkg_t *pkg;
+ struct archive_read_buffer buf;
ALPM_LOG_FUNC;
@@ -260,6 +260,9 @@ static int sync_db_read(pmdb_t *db, struct archive *archive, struct archive_entr
_alpm_log(PM_LOG_FUNCTION, "loading package data from archive entry %s\n",
entryname);
+ memset(&buf, 0, sizeof(buf));
+ buf.max_line_size = PATH_MAX;
+
/* get package and db file names */
STRDUP(pkgname, entryname, RET_ERR(PM_ERR_MEMORY, -1));
p = pkgname + strlen(pkgname);
@@ -279,8 +282,9 @@ static int sync_db_read(pmdb_t *db, struct archive *archive, struct archive_entr
if(strcmp(filename, "desc") == 0 || strcmp(filename, "depends") == 0
|| strcmp(filename, "deltas") == 0) {
- while(_alpm_archive_fgets(line, sizeof(line), archive) != NULL) {
- _alpm_strtrim(line);
+ while(_alpm_archive_fgets(archive, &buf) == ARCHIVE_OK) {
+ char *line = _alpm_strtrim(buf.line);
+
if(strcmp(line, "%NAME%") == 0) {
READ_NEXT(line);
if(strcmp(line, pkg->name) != 0) {
diff --git a/lib/libalpm/util.c b/lib/libalpm/util.c
index 1291ea0..b007ae6 100644
--- a/lib/libalpm/util.c
+++ b/lib/libalpm/util.c
@@ -771,33 +771,86 @@ int _alpm_test_md5sum(const char *filepath, const char *md5sum)
return(ret);
}
-char *_alpm_archive_fgets(char *line, size_t size, struct archive *a)
+/* Note: does NOT handle sparse files on purpose for speed. */
+int _alpm_archive_fgets(struct archive *a, struct archive_read_buffer *b)
{
- /* for now, just read one char at a time until we get to a
- * '\n' char. we can optimize this later with an internal
- * buffer. */
- /* leave room for zero terminator */
- char *last = line + size - 1;
- char *i;
-
- for(i = line; i < last; i++) {
- int ret = archive_read_data(a, i, 1);
- /* special check for first read- if null, return null,
- * this indicates EOF */
- if(i == line && (ret <= 0 || *i == '\0')) {
- return(NULL);
+ char *i = NULL;
+ int64_t offset;
+ int done = 0;
+
+ while(1) {
+ /* have we processed this entire block? */
+ if(b->block + b->block_size == b->block_offset) {
+ if(b->ret == ARCHIVE_EOF) {
+ /* reached end of archive on the last read, now we are out of data */
+ goto cleanup;
+ }
+
+ /* zero-copy- this is the entire next block of data. */
+ b->ret = archive_read_data_block(a, (void*)&b->block,
+ &b->block_size, &offset);
+ b->block_offset = b->block;
+
+ /* error or end of archive with no data read, cleanup */
+ if(b->ret < ARCHIVE_OK ||
+ (b->block_size == 0 && b->ret == ARCHIVE_EOF)) {
+ goto cleanup;
+ }
}
- /* check if read value was null or newline */
- if(ret <= 0 || *i == '\0' || *i == '\n') {
- last = i + 1;
- break;
+
+ /* loop through the block looking for EOL characters */
+ for(i = b->block_offset; i < b->block + b->block_size; i++) {
+ /* check if read value was null or newline */
+ if(*i == '\0' || *i == '\n') {
+ done = 1;
+ break;
+ }
}
- }
- /* always null terminate the buffer */
- *last = '\0';
+ /* allocate our buffer, or ensure our existing one is big enough */
+ if(!b->line) {
+ /* set the initial buffer to the read block_size */
+ CALLOC(b->line, b->block_size + 1, sizeof(char), RET_ERR(PM_ERR_MEMORY, -1));
+ b->line_size = b->block_size + 1;
+ b->line_offset = b->line;
+ } else {
+ size_t needed = (b->line_offset - b->line) + (i - b->block_offset) + 1;
+ if(needed > b->max_line_size) {
+ RET_ERR(PM_ERR_MEMORY, -1);
+ }
+ if(needed > b->line_size) {
+ /* need to realloc + copy data to fit total length */
+ char *new;
+ CALLOC(new, needed, sizeof(char), RET_ERR(PM_ERR_MEMORY, -1));
+ memcpy(new, b->line, b->line_size);
+ b->line_size = needed;
+ b->line_offset = new + (b->line_offset - b->line);
+ free(b->line);
+ b->line = new;
+ }
+ }
+
+ if(done) {
+ size_t len = i - b->block_offset;
+ memcpy(b->line_offset, b->block_offset, len);
+ b->line_offset[len] = '\0';
+ b->block_offset = ++i;
+ /* this is the main return point; from here you can read b->line */
+ return(ARCHIVE_OK);
+ } else {
+ /* we've looked through the whole block but no newline, copy it */
+ size_t len = b->block + b->block_size - b->block_offset;
+ memcpy(b->line_offset, b->block_offset, len);
+ }
+ }
- return(line);
+cleanup:
+ {
+ int ret = b->ret;
+ FREE(b->line);
+ memset(b, 0, sizeof(b));
+ return(ret);
+ }
}
int _alpm_splitname(const char *target, pmpkg_t *pkg)
diff --git a/lib/libalpm/util.h b/lib/libalpm/util.h
index 0b80420..dfdc6a7 100644
--- a/lib/libalpm/util.h
+++ b/lib/libalpm/util.h
@@ -59,6 +59,22 @@
_alpm_log(PM_LOG_DEBUG, "returning error %d from %s : %s\n", err, __func__, alpm_strerrorlast()); \
return(ret); } while(0)
+/**
+ * Used as a buffer/state holder for _alpm_archive_fgets().
+ */
+struct archive_read_buffer {
+ char *line;
+ char *line_offset;
+ size_t line_size;
+ size_t max_line_size;
+
+ char *block;
+ char *block_offset;
+ size_t block_size;
+
+ int ret;
+};
+
int _alpm_makepath(const char *path);
int _alpm_makepath_mode(const char *path, mode_t mode);
int _alpm_copyfile(const char *src, const char *dest);
@@ -76,7 +92,7 @@ char *_alpm_filecache_find(const char *filename);
const char *_alpm_filecache_setup(void);
int _alpm_lstat(const char *path, struct stat *buf);
int _alpm_test_md5sum(const char *filepath, const char *md5sum);
-char *_alpm_archive_fgets(char *line, size_t size, struct archive *a);
+int _alpm_archive_fgets(struct archive *a, struct archive_read_buffer *b);
int _alpm_splitname(const char *target, pmpkg_t *pkg);
unsigned long _alpm_hash_sdbm(const char *str);
--
1.7.3.3
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