Date: Thu, 20 Apr 2023 18:25:22 +0800
From: Tao Liu <ltao@redhat.com>
To: crash-utility@redhat.com
Subject: [Crash-utility] [PATCH v2] Replace lseek/read into pread for
        kcore and vmcore reading.
Message-ID: <20230420102521.33698-1-ltao@redhat.com>
Content-Type: text/plain; charset="US-ASCII"; x-default=true

Previously crash use lseek/read for kcore and vmcore reading, this involves 2
syscalls. And we can replace them with pread, only 1 syscall is needed for
kcore/vmcore reading, and we can have a better performance. Please note there
are plenty of places in crash using lseek/read, this patch doesn't modify all
of them, just the most commonly used kcore and diskdump vmcore reading.

Signed-off-by: Tao Liu <ltao@redhat.com>
---

v1 -> v2: add offset check before pread.

---
 diskdump.c | 31 +++++++++++++++++++++++++------
 netdump.c  | 19 ++++++++++++++-----
 2 files changed, 39 insertions(+), 11 deletions(-)

diff --git a/diskdump.c b/diskdump.c
index cf5f5d9..6ecd08a 100644
--- a/diskdump.c
+++ b/diskdump.c
@@ -515,16 +515,24 @@ arm_kdump_header_adjust(int header_version)
 static int
 read_pd(int fd, off_t offset, page_desc_t *pd)
 {
-       const off_t failed = (off_t)-1;
+       int ret;

        if (FLAT_FORMAT()) {
                if (!read_flattened_format(fd, offset, pd, sizeof(*pd)))
                        return READ_ERROR;
        } else {
-               if (lseek(fd, offset, SEEK_SET) == failed)
+               if (offset < 0) {
+                       if (CRASHDEBUG(8)) {
+                               fprintf(fp, "read_pd: invalid offset: %lx\n", offset);
+                       }
                        return SEEK_ERROR;
-               if (read(fd, pd, sizeof(*pd)) != sizeof(*pd))
+               }
+               if ((ret = pread(fd, pd, sizeof(*pd), offset)) != sizeof(*pd)) {
+                       if (ret == -1 && CRASHDEBUG(8)) {
+                               fprintf(fp, "read_pd: pread error: %s\n", strerror(errno));
+                       }
                        return READ_ERROR;
+               }
        }

        return 0;
@@ -1125,7 +1133,6 @@ cache_page(physaddr_t paddr)
        off_t seek_offset;
        page_desc_t pd;
        const int block_size = dd->block_size;
-       const off_t failed = (off_t)-1;
        ulong retlen;
 #ifdef ZSTD
        static ZSTD_DCtx *dctx = NULL;
@@ -1190,10 +1197,22 @@ cache_page(physaddr_t paddr)
                        return PAGE_INCOMPLETE;
                }
        } else {
-               if (lseek(dd->dfd, pd.offset, SEEK_SET) == failed)
+               if (pd.offset < 0) {
+                       if (CRASHDEBUG(8)) {
+                               fprintf(fp,
+                                       "read_diskdump/cache_page: "
+                                       "invalid offset: %lx\n", pd.offset);
+                       }
                        return SEEK_ERROR;
-               if (read(dd->dfd, dd->compressed_page, pd.size) != pd.size)
+               }
+               if ((ret = pread(dd->dfd, dd->compressed_page, pd.size, pd.offset)) != pd.size) {
+                       if (ret == -1 && CRASHDEBUG(8)) {
+                               fprintf(fp,
+                                       "read_diskdump/cache_page: "
+                                       "pread error: %s\n", strerror(errno));
+                       }
                        return READ_ERROR;
+               }
        }

        if (pd.flags & DUMP_DH_COMPRESSED_ZLIB) {
diff --git a/netdump.c b/netdump.c
index 01af145..696f5fd 100644
--- a/netdump.c
+++ b/netdump.c
@@ -4336,7 +4336,7 @@ no_nt_prstatus_exists:
 int
 read_proc_kcore(int fd, void *bufptr, int cnt, ulong addr, physaddr_t paddr)
 {
-       int i;
+       int i, ret;
        size_t readcnt;
        ulong kvaddr;
        Elf32_Phdr *lp32;
@@ -4436,11 +4436,20 @@ read_proc_kcore(int fd, void *bufptr, int cnt, ulong addr, physaddr_t paddr)
        if (offset == UNINITIALIZED)
                return SEEK_ERROR;

-        if (lseek(fd, offset, SEEK_SET) != offset)
-               perror("lseek");
-
-       if (read(fd, bufptr, readcnt) != readcnt)
+       if (offset < 0) {
+               if (CRASHDEBUG(8)) {
+                       fprintf(fp, "read_proc_kcore: "
+                               "invalid offset: %lx\n", offset);
+               }
+               return SEEK_ERROR;
+       }
+       if ((ret = pread(fd, bufptr, readcnt, offset)) != readcnt) {
+               if (ret == -1 && CRASHDEBUG(8)) {
+                       fprintf(fp, "read_proc_kcore: "
+                               "pread error: %s\n", strerror(errno));
+               }
                return READ_ERROR;
+       }

        return cnt;
 }

--
2.33.1