[PATCH v2 10/13] perf header: add a buffer to struct feat_fd

[David Carrillo-Cisneros]

Extend struct feat_fd to use a temporal buffer in pipe-mode, rather
than a perf.data file.

Revamp write_pmu_mappings to avoid seeking so that is compatible with
pipe-mode.

Print an error when trying to use buf in features that do not support
pipe-mode.

Signed-off-by: David Carrillo-Cisneros <davi...@google.com>
---
 tools/perf/util/header.c | 79 +++++++++++++++++++++++++++++++++++++-----------
 1 file changed, 62 insertions(+), 17 deletions(-)

diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
index 65cd2d1f1721..b7704b30ed52 100644
--- a/tools/perf/util/header.c
+++ b/tools/perf/util/header.c
@@ -60,6 +60,7 @@ struct perf_file_attr {
 struct feat_fd {
        struct perf_header *ph;
        int fd;
+       void *buf;      /* Either buf != NULL or fd >= 0 */
        ssize_t offset;
        size_t size;
 };
@@ -82,11 +83,27 @@ bool perf_header__has_feat(const struct perf_header 
*header, int feat)
 /* Return: 0 if succeded, -ERR if failed. */
 int do_write(struct feat_fd *fd, const void *buf, size_t size)
 {
-       ssize_t ret;
+       void *addr;
 
-       ret  = writen(fd->fd, buf, size);
-       if (ret != (ssize_t)size)
-               return ret < 0 ? (int)ret: -1;
+       if (!fd->buf) {
+               ssize_t ret = writen(fd->fd, buf, size);
+
+               if (ret != (ssize_t)size)
+                       return ret < 0 ? (int)ret : -1;
+               return 0;
+       }
+retry:
+       if (size > (fd->size - fd->offset)) {
+               addr = realloc(fd->buf, fd->size << 1);
+               if (!addr)
+                       return -ENOSPC;
+               fd->buf = addr;
+               fd->size <<= 1;
+               goto retry;
+       }
+
+       memcpy(fd->buf + fd->offset, buf, size);
+       fd->offset += size;
 
        return 0;
 }
@@ -126,10 +143,21 @@ static int do_write_string(struct feat_fd *fd, const char 
*str)
 
 static int __do_read(struct feat_fd *fd, void *addr, ssize_t size)
 {
-       ssize_t ret = readn(fd->fd, addr, size);
+       if (!fd->buf) {
+               ssize_t ret = readn(fd->fd, addr, size);
+
+               if (ret != (ssize_t)size)
+                       return ret < 0 ? (int)ret : -1;
+               return 0;
+       }
+
+       assert((ssize_t)fd->size > fd->offset);
+       if (size > (ssize_t)fd->size - fd->offset)
+               return -1;
+
+       memcpy(addr, fd->buf + fd->offset, size);
+       fd->offset += size;
 
-       if (ret != (ssize_t)size)
-               return ret < 0 ? (int)ret : -1;
        return 0;
 }
 
@@ -187,6 +215,10 @@ static char *do_read_string(struct feat_fd *fd)
 static int write_tracing_data(struct feat_fd *fd,
                              struct perf_evlist *evlist)
 {
+       if (fd->buf) {
+               pr_err("Unsupported write_tracing_data to memory buffer.\n");
+               return -1;
+       }
        return read_tracing_data(fd->fd, &evlist->entries);
 }
 
@@ -201,6 +233,10 @@ static int write_build_id(struct feat_fd *fd,
        if (!perf_session__read_build_ids(session, true))
                return -1;
 
+       if (fd->buf) {
+               pr_err("Unsupported write_build_id to memory buffer.\n");
+               return -1;
+       }
        err = perf_session__write_buildid_table(session, fd);
        if (err < 0) {
                pr_debug("failed to write buildid table\n");
@@ -795,11 +831,19 @@ static int write_pmu_mappings(struct feat_fd *fd,
                              struct perf_evlist *evlist __maybe_unused)
 {
        struct perf_pmu *pmu = NULL;
-       off_t offset = lseek(fd->fd, 0, SEEK_CUR);
-       __u32 pmu_num = 0;
+       u32 pmu_num = 0;
        int ret;
 
-       /* write real pmu_num later */
+       /*
+        * Do a first pass to count number of pmu to avoid lseek so this
+        * works in pipe mode as well.
+        */
+       while ((pmu = perf_pmu__scan(pmu))) {
+               if (!pmu->name)
+                       continue;
+               pmu_num++;
+       }
+
        ret = do_write(fd, &pmu_num, sizeof(pmu_num));
        if (ret < 0)
                return ret;
@@ -807,7 +851,6 @@ static int write_pmu_mappings(struct feat_fd *fd,
        while ((pmu = perf_pmu__scan(pmu))) {
                if (!pmu->name)
                        continue;
-               pmu_num++;
 
                ret = do_write(fd, &pmu->type, sizeof(pmu->type));
                if (ret < 0)
@@ -818,12 +861,6 @@ static int write_pmu_mappings(struct feat_fd *fd,
                        return ret;
        }
 
-       if (pwrite(fd->fd, &pmu_num, sizeof(pmu_num), offset) != 
sizeof(pmu_num)) {
-               /* discard all */
-               lseek(fd->fd, offset, SEEK_SET);
-               return -1;
-       }
-
        return 0;
 }
 
@@ -909,6 +946,10 @@ static int write_auxtrace(struct feat_fd *fd,
        struct perf_session *session;
        int err;
 
+       if (fd->buf) {
+               pr_err("Unsupported write_auxtrace to memory buffer.\n");
+               return -1;
+       }
        session = container_of(fd->ph, struct perf_session, header);
 
        err = auxtrace_index__write(fd->fd, &session->auxtrace_index);
@@ -2187,6 +2228,10 @@ static int do_write_feat(struct feat_fd *fd, struct 
perf_header *h, int type,
                if (!feat_ops[type].write)
                        return -1;
 
+               if (fd->buf) {
+                       pr_err("Called %s for memory buffer.\n", __func__);
+                       return -1;
+               }
                (*p)->offset = lseek(fd->fd, 0, SEEK_CUR);
 
                err = feat_ops[type].write(fd, evlist);
-- 
2.13.0.219.gdb65acc882-goog