* [PATCH RESEND 1/3] initramfs: move unnecessary memcmp from hot path
@ 2021-07-21 11:51 David Disseldorp
2021-07-21 11:51 ` [PATCH RESEND 2/3] initramfs: print helpful cpio error on "crc" magic David Disseldorp
` (2 more replies)
0 siblings, 3 replies; 6+ messages in thread
From: David Disseldorp @ 2021-07-21 11:51 UTC (permalink / raw)
To: linux-fsdevel, linux-doc; +Cc: Matthew Wilcox, Al Viro, David Disseldorp
do_header() is called for each cpio entry and first checks for "newc"
magic before parsing further. The magic check includes a special case
error message if POSIX.1 ASCII (cpio -H odc) magic is detected. This
special case POSIX.1 check needn't be done in the hot path, so move it
under the non-newc-magic error path.
Signed-off-by: David Disseldorp <ddiss@suse.de>
---
init/initramfs.c | 9 ++++-----
1 file changed, 4 insertions(+), 5 deletions(-)
diff --git a/init/initramfs.c b/init/initramfs.c
index af27abc59643..f01590cefa2d 100644
--- a/init/initramfs.c
+++ b/init/initramfs.c
@@ -256,12 +256,11 @@ static int __init do_collect(void)
static int __init do_header(void)
{
- if (memcmp(collected, "070707", 6)==0) {
- error("incorrect cpio method used: use -H newc option");
- return 1;
- }
if (memcmp(collected, "070701", 6)) {
- error("no cpio magic");
+ if (memcmp(collected, "070707", 6) == 0)
+ error("incorrect cpio method used: use -H newc option");
+ else
+ error("no cpio magic");
return 1;
}
parse_header(collected);
--
2.26.2
^ permalink raw reply related [flat|nested] 6+ messages in thread
* [PATCH RESEND 2/3] initramfs: print helpful cpio error on "crc" magic
2021-07-21 11:51 [PATCH RESEND 1/3] initramfs: move unnecessary memcmp from hot path David Disseldorp
@ 2021-07-21 11:51 ` David Disseldorp
2021-07-21 11:51 ` [PATCH v2 3/3] docs: remove mention of "crc" cpio format support David Disseldorp
2021-08-04 9:31 ` [PATCH RESEND 1/3] initramfs: move unnecessary memcmp from hot path David Disseldorp
2 siblings, 0 replies; 6+ messages in thread
From: David Disseldorp @ 2021-07-21 11:51 UTC (permalink / raw)
To: linux-fsdevel, linux-doc; +Cc: Matthew Wilcox, Al Viro, David Disseldorp
Contrary to the buffer-format.rst documentation, initramfs cpio
extraction does not support "crc" archives, which carry "070702"
header magic. Make it a little clearer that "newc" (magic="070701") is
the only supported cpio format, by extending the POSIX.1 ASCII
(magic="070707") specific error message to also cover "crc" magic.
Signed-off-by: David Disseldorp <ddiss@suse.de>
---
init/initramfs.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/init/initramfs.c b/init/initramfs.c
index f01590cefa2d..19b1c70446fc 100644
--- a/init/initramfs.c
+++ b/init/initramfs.c
@@ -257,7 +257,7 @@ static int __init do_collect(void)
static int __init do_header(void)
{
if (memcmp(collected, "070701", 6)) {
- if (memcmp(collected, "070707", 6) == 0)
+ if (memcmp(collected, "0707", 4) == 0)
error("incorrect cpio method used: use -H newc option");
else
error("no cpio magic");
--
2.26.2
^ permalink raw reply related [flat|nested] 6+ messages in thread
* [PATCH v2 3/3] docs: remove mention of "crc" cpio format support
2021-07-21 11:51 [PATCH RESEND 1/3] initramfs: move unnecessary memcmp from hot path David Disseldorp
2021-07-21 11:51 ` [PATCH RESEND 2/3] initramfs: print helpful cpio error on "crc" magic David Disseldorp
@ 2021-07-21 11:51 ` David Disseldorp
2021-08-04 9:31 ` [PATCH RESEND 1/3] initramfs: move unnecessary memcmp from hot path David Disseldorp
2 siblings, 0 replies; 6+ messages in thread
From: David Disseldorp @ 2021-07-21 11:51 UTC (permalink / raw)
To: linux-fsdevel, linux-doc; +Cc: Matthew Wilcox, Al Viro, David Disseldorp
init/initramfs.c only supports extraction of cpio archives carrying the
"newc" header magic ("070701"). Remove statements indicating support for
the "crc" cpio format.
Signed-off-by: David Disseldorp <ddiss@suse.de>
---
.../early-userspace/buffer-format.rst | 24 +++++++------------
1 file changed, 8 insertions(+), 16 deletions(-)
Version 2:
- reword initramfs padding description, as suggested by Matthew Wilcox
diff --git a/Documentation/driver-api/early-userspace/buffer-format.rst b/Documentation/driver-api/early-userspace/buffer-format.rst
index 7f74e301fdf3..0df76bca444c 100644
--- a/Documentation/driver-api/early-userspace/buffer-format.rst
+++ b/Documentation/driver-api/early-userspace/buffer-format.rst
@@ -14,10 +14,10 @@ is different. The initramfs buffer contains an archive which is
expanded into a ramfs filesystem; this document details the format of
the initramfs buffer format.
-The initramfs buffer format is based around the "newc" or "crc" CPIO
-formats, and can be created with the cpio(1) utility. The cpio
-archive can be compressed using gzip(1). One valid version of an
-initramfs buffer is thus a single .cpio.gz file.
+The initramfs buffer format is based around the "newc" CPIO format, and
+can be created with the cpio(1) utility. The cpio archive can be
+compressed using gzip(1). One valid version of an initramfs buffer is
+thus a single .cpio.gz file.
The full format of the initramfs buffer is defined by the following
grammar, where::
@@ -40,9 +40,8 @@ grammar, where::
In human terms, the initramfs buffer contains a collection of
-compressed and/or uncompressed cpio archives (in the "newc" or "crc"
-formats); arbitrary amounts zero bytes (for padding) can be added
-between members.
+compressed and/or uncompressed cpio archives (in the "newc" format),
+with arbitrary amount of zero-byte padding between members.
The cpio "TRAILER!!!" entry (cpio end-of-archive) is optional, but is
not ignored; see "handling of hard links" below.
@@ -55,7 +54,7 @@ by the ASCII string "000012ac"):
============= ================== ==============================================
Field name Field size Meaning
============= ================== ==============================================
-c_magic 6 bytes The string "070701" or "070702"
+c_magic 6 bytes The string "070701"
c_ino 8 bytes File inode number
c_mode 8 bytes File mode and permissions
c_uid 8 bytes File uid
@@ -68,8 +67,7 @@ c_min 8 bytes Minor part of file device number
c_rmaj 8 bytes Major part of device node reference
c_rmin 8 bytes Minor part of device node reference
c_namesize 8 bytes Length of filename, including final \0
-c_chksum 8 bytes Checksum of data field if c_magic is 070702;
- otherwise zero
+c_chksum 8 bytes Ignored; reserved for unsupported "crc" format
============= ================== ==============================================
The c_mode field matches the contents of st_mode returned by stat(2)
@@ -78,12 +76,6 @@ on Linux, and encodes the file type and file permissions.
The c_filesize should be zero for any file which is not a regular file
or symlink.
-The c_chksum field contains a simple 32-bit unsigned sum of all the
-bytes in the data field. cpio(1) refers to this as "crc", which is
-clearly incorrect (a cyclic redundancy check is a different and
-significantly stronger integrity check), however, this is the
-algorithm used.
-
If the filename is "TRAILER!!!" this is actually an end-of-archive
marker; the c_filesize for an end-of-archive marker must be zero.
--
2.26.2
^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [PATCH RESEND 1/3] initramfs: move unnecessary memcmp from hot path
2021-07-21 11:51 [PATCH RESEND 1/3] initramfs: move unnecessary memcmp from hot path David Disseldorp
2021-07-21 11:51 ` [PATCH RESEND 2/3] initramfs: print helpful cpio error on "crc" magic David Disseldorp
2021-07-21 11:51 ` [PATCH v2 3/3] docs: remove mention of "crc" cpio format support David Disseldorp
@ 2021-08-04 9:31 ` David Disseldorp
2021-08-04 12:57 ` Al Viro
2 siblings, 1 reply; 6+ messages in thread
From: David Disseldorp @ 2021-08-04 9:31 UTC (permalink / raw)
To: linux-fsdevel, linux-doc; +Cc: Matthew Wilcox, Al Viro
Ping, any feedback on this change?
I think it's a no brainer, but for kicks I ran a few unrealistic micro
benchmarks on my laptop. Extraction time for a cpio image with 1M+
directories improved by 5ms (pre: 14.614s, post: 14.609s), when averaged
across 20 runs of:
qemu-system-x86_64 -machine accel=kvm -smp cpus=1 -m 10240 \
-kernel ~/linux/arch/x86/boot/bzImage \
-initrd ./initrds/gen_cpio.out \
-append "initramfs_async=0 console=ttyS0 panic=0" -nographic \
| awk '/Trying to unpack rootfs/ {start_ts = $2};
/Freeing initrd memory/ {end_ts = $2}
END {printf "%f\n", end_ts - start_ts}'
Cheers, David
On Wed, 21 Jul 2021 13:51:51 +0200, David Disseldorp wrote:
> do_header() is called for each cpio entry and first checks for "newc"
> magic before parsing further. The magic check includes a special case
> error message if POSIX.1 ASCII (cpio -H odc) magic is detected. This
> special case POSIX.1 check needn't be done in the hot path, so move it
> under the non-newc-magic error path.
>
> Signed-off-by: David Disseldorp <ddiss@suse.de>
> ---
> init/initramfs.c | 9 ++++-----
> 1 file changed, 4 insertions(+), 5 deletions(-)
>
> diff --git a/init/initramfs.c b/init/initramfs.c
> index af27abc59643..f01590cefa2d 100644
> --- a/init/initramfs.c
> +++ b/init/initramfs.c
> @@ -256,12 +256,11 @@ static int __init do_collect(void)
>
> static int __init do_header(void)
> {
> - if (memcmp(collected, "070707", 6)==0) {
> - error("incorrect cpio method used: use -H newc option");
> - return 1;
> - }
> if (memcmp(collected, "070701", 6)) {
> - error("no cpio magic");
> + if (memcmp(collected, "070707", 6) == 0)
> + error("incorrect cpio method used: use -H newc option");
> + else
> + error("no cpio magic");
> return 1;
> }
> parse_header(collected);
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH RESEND 1/3] initramfs: move unnecessary memcmp from hot path
2021-08-04 9:31 ` [PATCH RESEND 1/3] initramfs: move unnecessary memcmp from hot path David Disseldorp
@ 2021-08-04 12:57 ` Al Viro
2021-08-04 13:37 ` David Disseldorp
0 siblings, 1 reply; 6+ messages in thread
From: Al Viro @ 2021-08-04 12:57 UTC (permalink / raw)
To: David Disseldorp; +Cc: linux-fsdevel, linux-doc, Matthew Wilcox
On Wed, Aug 04, 2021 at 11:31:29AM +0200, David Disseldorp wrote:
> Ping, any feedback on this change?
>
> I think it's a no brainer, but for kicks I ran a few unrealistic micro
> benchmarks on my laptop. Extraction time for a cpio image with 1M+
> directories improved by 5ms (pre: 14.614s, post: 14.609s), when averaged
> across 20 runs of:
> qemu-system-x86_64 -machine accel=kvm -smp cpus=1 -m 10240 \
> -kernel ~/linux/arch/x86/boot/bzImage \
> -initrd ./initrds/gen_cpio.out \
> -append "initramfs_async=0 console=ttyS0 panic=0" -nographic \
> | awk '/Trying to unpack rootfs/ {start_ts = $2};
> /Freeing initrd memory/ {end_ts = $2}
> END {printf "%f\n", end_ts - start_ts}'
What was the dispersion for those runs?
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH RESEND 1/3] initramfs: move unnecessary memcmp from hot path
2021-08-04 12:57 ` Al Viro
@ 2021-08-04 13:37 ` David Disseldorp
0 siblings, 0 replies; 6+ messages in thread
From: David Disseldorp @ 2021-08-04 13:37 UTC (permalink / raw)
To: Al Viro; +Cc: linux-fsdevel, linux-doc, Matthew Wilcox
On Wed, 4 Aug 2021 12:57:16 +0000, Al Viro wrote:
> On Wed, Aug 04, 2021 at 11:31:29AM +0200, David Disseldorp wrote:
> > Ping, any feedback on this change?
> >
> > I think it's a no brainer, but for kicks I ran a few unrealistic micro
> > benchmarks on my laptop. Extraction time for a cpio image with 1M+
> > directories improved by 5ms (pre: 14.614s, post: 14.609s), when averaged
> > across 20 runs of:
> > qemu-system-x86_64 -machine accel=kvm -smp cpus=1 -m 10240 \
> > -kernel ~/linux/arch/x86/boot/bzImage \
> > -initrd ./initrds/gen_cpio.out \
> > -append "initramfs_async=0 console=ttyS0 panic=0" -nographic \
> > | awk '/Trying to unpack rootfs/ {start_ts = $2};
> > /Freeing initrd memory/ {end_ts = $2}
> > END {printf "%f\n", end_ts - start_ts}'
>
> What was the dispersion for those runs?
Too high for the 5ms to be considered statistically significant. Std
deviations were pre: 171ms, post: 214ms... <sigh> I'll redo this on a
proper test rig.
Cheers, David
^ permalink raw reply [flat|nested] 6+ messages in thread
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2021-07-21 11:51 [PATCH RESEND 1/3] initramfs: move unnecessary memcmp from hot path David Disseldorp
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2021-07-21 11:51 ` [PATCH v2 3/3] docs: remove mention of "crc" cpio format support David Disseldorp
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