Re: [Crash-utility] [PATCH 5/5] [RFC] Replace lseek/read into pread for kcore and vmcore reading.
On 2023/03/25 13:12, Tao Liu wrote:
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.
This is nice as an optimization, but can we distinguish a seek error and
read error with errno as currently we can do?
Thanks,
Kazu
>
> Signed-off-by: Tao Liu <ltao(a)redhat.com>
> ---
> diskdump.c | 11 ++---------
> netdump.c | 5 +----
> 2 files changed, 3 insertions(+), 13 deletions(-)
>
> diff --git a/diskdump.c b/diskdump.c
> index cf5f5d9..acf79f2 100644
> --- a/diskdump.c
> +++ b/diskdump.c
> @@ -515,15 +515,11 @@ 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;
> -
> if (FLAT_FORMAT()) {
> if (!read_flattened_format(fd, offset, pd, sizeof(*pd)))
> return READ_ERROR;
> } else {
> - if (lseek(fd, offset, SEEK_SET) == failed)
> - return SEEK_ERROR;
> - if (read(fd, pd, sizeof(*pd)) != sizeof(*pd))
> + if (pread(fd, pd, sizeof(*pd), offset) != sizeof(*pd))
> return READ_ERROR;
> }
>
> @@ -1125,7 +1121,6 @@ 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;
> @@ -1190,9 +1185,7 @@ cache_page(physaddr_t paddr)
> return PAGE_INCOMPLETE;
> }
> } else {
> - if (lseek(dd->dfd, pd.offset, SEEK_SET) == failed)
> - return SEEK_ERROR;
> - if (read(dd->dfd, dd->compressed_page, pd.size) != pd.size)
> + if (pread(dd->dfd, dd->compressed_page, pd.size, pd.offset) != pd.size)
> return READ_ERROR;
> }
>
> diff --git a/netdump.c b/netdump.c
> index 01af145..e76807a 100644
> --- a/netdump.c
> +++ b/netdump.c
> @@ -4436,10 +4436,7 @@ 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 (pread(fd, bufptr, readcnt, offset) != readcnt)
> return READ_ERROR;
>
> return cnt;