new behaviour in git merge

new behaviour in git merge

[Stephen Rothwell]

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Hi all,

I am not sure when this started, but I think git has changed its behaviour
when merging.   As you all know, I do a lot of merging of trees for
linux-next each day.  Today I noticed that when I merge a tree, sometimes
the timestamps are modified for files that are not modified on one side
of the merge.  It is not consistent and it is not all the files that are
modified on the HEAD side (relative to the merge-base).

For example, today when I merged the drm tree:

$ git merge drm/drm-next
Auto-merging drivers/gpu/drm/drm_info.c
Removing drivers/gpu/drm/i830/Makefile
Removing drivers/gpu/drm/i830/i830_dma.c
Removing drivers/gpu/drm/i830/i830_drv.c
Removing drivers/gpu/drm/i830/i830_drv.h
Removing drivers/gpu/drm/i830/i830_irq.c
Auto-merging drivers/gpu/drm/i915/i915_drv.c
Auto-merging drivers/gpu/drm/i915/i915_drv.h
Auto-merging drivers/gpu/drm/i915/intel_sdvo.c
Auto-merging drivers/gpu/drm/radeon/atombios_crtc.c
Auto-merging drivers/gpu/drm/radeon/evergreen_blit_kms.c
Auto-merging drivers/gpu/drm/radeon/r600.c
Auto-merging drivers/gpu/drm/radeon/r600_blit_kms.c
Auto-merging drivers/gpu/drm/radeon/r600_cs.c
Auto-merging drivers/gpu/drm/radeon/r600d.h
Auto-merging drivers/gpu/drm/radeon/radeon_device.c
Auto-merging drivers/gpu/drm/radeon/radeon_display.c
Auto-merging drivers/gpu/drm/radeon/radeon_mode.h
Auto-merging drivers/gpu/drm/radeon/radeon_ttm.c
Auto-merging drivers/gpu/drm/radeon/rv770.c
Removing include/drm/i830_drm.h
Merge made by recursive.
 drivers/gpu/drm/Kconfig                     |   47 +-
 drivers/gpu/drm/Makefile                    |    3 +-
 drivers/gpu/drm/drm_crtc.c                  |   33 +
 drivers/gpu/drm/drm_drv.c                   |   48 +-
 drivers/gpu/drm/drm_edid.c                  |   19 +-
 drivers/gpu/drm/drm_edid_modes.h            |    4 +-
 drivers/gpu/drm/drm_fb_helper.c             |    5 +
 drivers/gpu/drm/drm_gem.c                   |    5 +-
 drivers/gpu/drm/drm_hashtab.c               |   27 +-
 drivers/gpu/drm/drm_info.c                  |   27 +-
 drivers/gpu/drm/drm_ioctl.c                 |  115 +--
 drivers/gpu/drm/drm_irq.c                   |   14 +-
 drivers/gpu/drm/drm_mm.c                    |  570 ++++++-----
 drivers/gpu/drm/drm_modes.c                 |    6 +-
 drivers/gpu/drm/drm_pci.c                   |  205 ++++-
 drivers/gpu/drm/drm_platform.c              |   75 ++-
 drivers/gpu/drm/drm_stub.c                  |   21 +-
 drivers/gpu/drm/drm_usb.c                   |  117 ++
 drivers/gpu/drm/i810/i810_dma.c             |   18 +-
 drivers/gpu/drm/i810/i810_drv.c             |   20 +-
 drivers/gpu/drm/i830/Makefile               |    8 -
 drivers/gpu/drm/i830/i830_dma.c             | 1560 ---------------------------
 drivers/gpu/drm/i830/i830_drv.c             |  107 --
 drivers/gpu/drm/i830/i830_drv.h             |  295 -----
 drivers/gpu/drm/i830/i830_irq.c             |  186 ----
 drivers/gpu/drm/i915/i915_drv.c             |   23 +-
 drivers/gpu/drm/i915/i915_drv.h             |    7 +
 drivers/gpu/drm/i915/i915_gem.c             |  103 ++-
 drivers/gpu/drm/i915/intel_sdvo.c           |    2 +-
 drivers/gpu/drm/mga/mga_dma.c               |    2 +-
 drivers/gpu/drm/mga/mga_drv.c               |   13 +-
 drivers/gpu/drm/nouveau/nouveau_drv.c       |   21 +-
 drivers/gpu/drm/nouveau/nouveau_mem.c       |    2 +-
 drivers/gpu/drm/nouveau/nouveau_object.c    |    2 +-
 drivers/gpu/drm/nouveau/nouveau_sgdma.c     |   31 +-
 drivers/gpu/drm/nouveau/nouveau_state.c     |    4 +-
 drivers/gpu/drm/nouveau/nv17_tv.c           |    4 +-
 drivers/gpu/drm/nouveau/nv17_tv.h           |    2 +-
 drivers/gpu/drm/nouveau/nv17_tv_modes.c     |    2 +-
 drivers/gpu/drm/nouveau/nv50_instmem.c      |    4 +-
 drivers/gpu/drm/nouveau/nvc0_instmem.c      |    2 +-
 drivers/gpu/drm/r128/r128_drv.c             |   14 +-
 drivers/gpu/drm/radeon/atombios_crtc.c      |    8 +-
 drivers/gpu/drm/radeon/evergreen_blit_kms.c |    2 +-
 drivers/gpu/drm/radeon/r600.c               |    2 +-
 drivers/gpu/drm/radeon/r600_audio.c         |    1 +
 drivers/gpu/drm/radeon/r600_blit_kms.c      |    2 +-
 drivers/gpu/drm/radeon/r600_cs.c            |  353 ++++--
 drivers/gpu/drm/radeon/r600_hdmi.c          |    1 +
 drivers/gpu/drm/radeon/r600d.h              |    5 +
 drivers/gpu/drm/radeon/radeon.h             |   90 +--
 drivers/gpu/drm/radeon/radeon_asic.h        |   77 ++-
 drivers/gpu/drm/radeon/radeon_benchmark.c   |    4 +-
 drivers/gpu/drm/radeon/radeon_cp.c          |    4 +-
 drivers/gpu/drm/radeon/radeon_cs.c          |    2 +-
 drivers/gpu/drm/radeon/radeon_device.c      |    4 +-
 drivers/gpu/drm/radeon/radeon_display.c     |    4 +-
 drivers/gpu/drm/radeon/radeon_drv.c         |   49 +-
 drivers/gpu/drm/radeon/radeon_fb.c          |   12 +-
 drivers/gpu/drm/radeon/radeon_gart.c        |   38 +-
 drivers/gpu/drm/radeon/radeon_gem.c         |   96 ++-
 drivers/gpu/drm/radeon/radeon_kms.c         |    4 +-
 drivers/gpu/drm/radeon/radeon_legacy_crtc.c |    4 +-
 drivers/gpu/drm/radeon/radeon_mode.h        |    1 +
 drivers/gpu/drm/radeon/radeon_object.c      |   28 +-
 drivers/gpu/drm/radeon/radeon_object.h      |    7 +-
 drivers/gpu/drm/radeon/radeon_ring.c        |    4 +-
 drivers/gpu/drm/radeon/radeon_test.c        |    4 +-
 drivers/gpu/drm/radeon/radeon_ttm.c         |   10 +-
 drivers/gpu/drm/radeon/rv770.c              |    2 +-
 drivers/gpu/drm/savage/savage_drv.c         |   14 +-
 drivers/gpu/drm/sis/sis_drv.c               |   13 +-
 drivers/gpu/drm/tdfx/tdfx_drv.c             |   13 +-
 drivers/gpu/drm/ttm/ttm_agp_backend.c       |    3 +-
 drivers/gpu/drm/ttm/ttm_bo.c                |    3 +-
 drivers/gpu/drm/ttm/ttm_page_alloc.c        |   34 +-
 drivers/gpu/drm/ttm/ttm_tt.c                |   12 +-
 drivers/gpu/drm/via/via_drv.c               |   13 +-
 drivers/gpu/drm/vmwgfx/vmwgfx_buffer.c      |    3 +-
 drivers/gpu/drm/vmwgfx/vmwgfx_drv.c         |   23 +-
 drivers/gpu/drm/vmwgfx/vmwgfx_ldu.c         |    5 +-
 include/drm/Kbuild                          |    1 -
 include/drm/drm.h                           |    4 +
 include/drm/drmP.h                          |  120 ++-
 include/drm/drm_crtc.h                      |   13 +-
 include/drm/drm_hashtab.h                   |    6 +-
 include/drm/drm_mm.h                        |   49 +-
 include/drm/drm_mode.h                      |   29 +
 include/drm/drm_usb.h                       |   15 +
 include/drm/i830_drm.h                      |  342 ------
 include/drm/ttm/ttm_bo_driver.h             |    6 +-
 include/drm/ttm/ttm_page_alloc.h            |    8 +-
 92 files changed, 1755 insertions(+), 3565 deletions(-)
 create mode 100644 drivers/gpu/drm/drm_usb.c
 delete mode 100644 drivers/gpu/drm/i830/Makefile
 delete mode 100644 drivers/gpu/drm/i830/i830_dma.c
 delete mode 100644 drivers/gpu/drm/i830/i830_drv.c
 delete mode 100644 drivers/gpu/drm/i830/i830_drv.h
 delete mode 100644 drivers/gpu/drm/i830/i830_irq.c
 create mode 100644 include/drm/drm_usb.h
 delete mode 100644 include/drm/i830_drm.h

Then the timestamps on all these files were updated (this is the list of
files rsync has decided to copy - I checked and the timestamps are indeed
modified):

Documentation/devicetree/booting-without-of.txt
Documentation/devicetree/bindings/eeprom.txt
Documentation/devicetree/bindings/marvell.txt
Documentation/devicetree/bindings/xilinx.txt
Documentation/devicetree/bindings/ata/fsl-sata.txt
Documentation/devicetree/bindings/gpio/8xxx_gpio.txt
Documentation/devicetree/bindings/gpio/gpio.txt
Documentation/devicetree/bindings/gpio/led.txt
Documentation/devicetree/bindings/i2c/fsl-i2c.txt
Documentation/devicetree/bindings/mmc/fsl-esdhc.txt
Documentation/devicetree/bindings/mmc/mmc-spi-slot.txt
Documentation/devicetree/bindings/mtd/fsl-upm-nand.txt
Documentation/devicetree/bindings/mtd/mtd-physmap.txt
Documentation/devicetree/bindings/net/fsl-tsec-phy.txt
Documentation/devicetree/bindings/net/mdio-gpio.txt
Documentation/devicetree/bindings/net/phy.txt
Documentation/devicetree/bindings/net/can/mpc5xxx-mscan.txt
Documentation/devicetree/bindings/net/can/sja1000.txt
Documentation/devicetree/bindings/pci/83xx-512x-pci.txt
Documentation/devicetree/bindings/powerpc/4xx/cpm.txt
Documentation/devicetree/bindings/powerpc/4xx/emac.txt
Documentation/devicetree/bindings/powerpc/4xx/ndfc.txt
Documentation/devicetree/bindings/powerpc/4xx/ppc440spe-adma.txt
Documentation/devicetree/bindings/powerpc/4xx/reboot.txt
Documentation/devicetree/bindings/powerpc/fsl/board.txt
Documentation/devicetree/bindings/powerpc/fsl/diu.txt
Documentation/devicetree/bindings/powerpc/fsl/dma.txt
Documentation/devicetree/bindings/powerpc/fsl/ecm.txt
Documentation/devicetree/bindings/powerpc/fsl/gtm.txt
Documentation/devicetree/bindings/powerpc/fsl/guts.txt
Documentation/devicetree/bindings/powerpc/fsl/lbc.txt
Documentation/devicetree/bindings/powerpc/fsl/mcm.txt
Documentation/devicetree/bindings/powerpc/fsl/mcu-mpc8349emitx.txt
Documentation/devicetree/bindings/powerpc/fsl/mpc5121-psc.txt
Documentation/devicetree/bindings/powerpc/fsl/mpc5200.txt
Documentation/devicetree/bindings/powerpc/fsl/mpic.txt
Documentation/devicetree/bindings/powerpc/fsl/msi-pic.txt
Documentation/devicetree/bindings/powerpc/fsl/pmc.txt
Documentation/devicetree/bindings/powerpc/fsl/sec.txt
Documentation/devicetree/bindings/powerpc/fsl/ssi.txt
Documentation/devicetree/bindings/powerpc/fsl/cpm_qe/cpm.txt
Documentation/devicetree/bindings/powerpc/fsl/cpm_qe/gpio.txt
Documentation/devicetree/bindings/powerpc/fsl/cpm_qe/network.txt
Documentation/devicetree/bindings/powerpc/fsl/cpm_qe/qe.txt
Documentation/devicetree/bindings/powerpc/fsl/cpm_qe/serial.txt
Documentation/devicetree/bindings/powerpc/fsl/cpm_qe/cpm/brg.txt
Documentation/devicetree/bindings/powerpc/fsl/cpm_qe/cpm/i2c.txt
Documentation/devicetree/bindings/powerpc/fsl/cpm_qe/cpm/pic.txt
Documentation/devicetree/bindings/powerpc/fsl/cpm_qe/cpm/usb.txt
Documentation/devicetree/bindings/powerpc/fsl/cpm_qe/qe/firmware.txt
Documentation/devicetree/bindings/powerpc/fsl/cpm_qe/qe/par_io.txt
Documentation/devicetree/bindings/powerpc/fsl/cpm_qe/qe/pincfg.txt
Documentation/devicetree/bindings/powerpc/fsl/cpm_qe/qe/ucc.txt
Documentation/devicetree/bindings/powerpc/fsl/cpm_qe/qe/usb.txt
Documentation/devicetree/bindings/powerpc/nintendo/gamecube.txt
Documentation/devicetree/bindings/powerpc/nintendo/wii.txt
Documentation/devicetree/bindings/spi/fsl-spi.txt
Documentation/devicetree/bindings/spi/spi-bus.txt
Documentation/devicetree/bindings/usb/fsl-usb.txt
Documentation/devicetree/bindings/usb/usb-ehci.txt
Documentation/laptops/hpfall.c
Documentation/misc-devices/lis3lv02d
arch/arm/mach-exynos4/Kconfig
arch/arm/mach-exynos4/Makefile.boot
arch/arm/mach-exynos4/clock.c
arch/arm/mach-exynos4/cpu.c
arch/arm/mach-exynos4/cpufreq.c
arch/arm/mach-exynos4/dev-audio.c
arch/arm/mach-exynos4/dev-pd.c
arch/arm/mach-exynos4/dev-sysmmu.c
arch/arm/mach-exynos4/dma.c
arch/arm/mach-exynos4/gpiolib.c
arch/arm/mach-exynos4/headsmp.S
arch/arm/mach-exynos4/hotplug.c
arch/arm/mach-exynos4/init.c
arch/arm/mach-exynos4/irq-combiner.c
arch/arm/mach-exynos4/irq-eint.c
arch/arm/mach-exynos4/localtimer.c
arch/arm/mach-exynos4/mach-smdkc210.c
arch/arm/mach-exynos4/mach-smdkv310.c
arch/arm/mach-exynos4/mach-universal_c210.c
arch/arm/mach-exynos4/platsmp.c
arch/arm/mach-exynos4/setup-i2c0.c
arch/arm/mach-exynos4/setup-i2c1.c
arch/arm/mach-exynos4/setup-i2c2.c
arch/arm/mach-exynos4/setup-i2c3.c
arch/arm/mach-exynos4/setup-i2c4.c
arch/arm/mach-exynos4/setup-i2c5.c
arch/arm/mach-exynos4/setup-i2c6.c
arch/arm/mach-exynos4/setup-i2c7.c
arch/arm/mach-exynos4/setup-sdhci-gpio.c
arch/arm/mach-exynos4/setup-sdhci.c
arch/arm/mach-exynos4/time.c
arch/arm/mach-exynos4/include/mach/debug-macro.S
arch/arm/mach-exynos4/include/mach/entry-macro.S
arch/arm/mach-exynos4/include/mach/hardware.h
arch/arm/mach-exynos4/include/mach/io.h
arch/arm/mach-exynos4/include/mach/irqs.h
arch/arm/mach-exynos4/include/mach/memory.h
arch/arm/mach-exynos4/include/mach/pwm-clock.h
arch/arm/mach-exynos4/include/mach/regs-clock.h
arch/arm/mach-exynos4/include/mach/regs-irq.h
arch/arm/mach-exynos4/include/mach/regs-mem.h
arch/arm/mach-exynos4/include/mach/regs-pmu.h
arch/arm/mach-exynos4/include/mach/regs-sysmmu.h
arch/arm/mach-exynos4/include/mach/smp.h
arch/arm/mach-exynos4/include/mach/sysmmu.h
arch/arm/mach-exynos4/include/mach/system.h
arch/arm/mach-exynos4/include/mach/timex.h
arch/arm/mach-exynos4/include/mach/uncompress.h
arch/arm/mach-exynos4/include/mach/vmalloc.h
arch/arm/mach-msm/devices-iommu.c
arch/arm/mach-mx5/devices-imx50.h
arch/arm/mach-vt8500/include/mach/vmalloc.h
arch/arm/plat-versatile/headsmp.S
arch/arm/plat-versatile/localtimer.c
drivers/char/virtio_console.c
deleting drivers/gpu/drm/i830/i830_irq.c
deleting drivers/gpu/drm/i830/i830_drv.h
deleting drivers/gpu/drm/i830/i830_drv.c
deleting drivers/gpu/drm/i830/i830_dma.c
deleting drivers/gpu/drm/i830/Makefile
drivers/gpu/drm/Kconfig
drivers/gpu/drm/Makefile
drivers/gpu/drm/drm_crtc.c
drivers/gpu/drm/drm_drv.c
drivers/gpu/drm/drm_edid.c
drivers/gpu/drm/drm_edid_modes.h
drivers/gpu/drm/drm_fb_helper.c
drivers/gpu/drm/drm_gem.c
drivers/gpu/drm/drm_hashtab.c
drivers/gpu/drm/drm_info.c
drivers/gpu/drm/drm_ioctl.c
drivers/gpu/drm/drm_irq.c
drivers/gpu/drm/drm_mm.c
drivers/gpu/drm/drm_modes.c
drivers/gpu/drm/drm_pci.c
drivers/gpu/drm/drm_platform.c
drivers/gpu/drm/drm_stub.c
drivers/gpu/drm/drm_usb.c
drivers/gpu/drm/i810/i810_dma.c
drivers/gpu/drm/i810/i810_drv.c
drivers/gpu/drm/i915/i915_drv.c
drivers/gpu/drm/i915/i915_drv.h
drivers/gpu/drm/i915/i915_gem.c
drivers/gpu/drm/i915/intel_sdvo.c
drivers/gpu/drm/mga/mga_dma.c
drivers/gpu/drm/mga/mga_drv.c
drivers/gpu/drm/nouveau/nouveau_drv.c
drivers/gpu/drm/nouveau/nouveau_mem.c
drivers/gpu/drm/nouveau/nouveau_object.c
drivers/gpu/drm/nouveau/nouveau_sgdma.c
drivers/gpu/drm/nouveau/nouveau_state.c
drivers/gpu/drm/nouveau/nv17_tv.c
drivers/gpu/drm/nouveau/nv17_tv.h
drivers/gpu/drm/nouveau/nv17_tv_modes.c
drivers/gpu/drm/nouveau/nv50_instmem.c
drivers/gpu/drm/nouveau/nvc0_instmem.c
drivers/gpu/drm/r128/r128_drv.c
drivers/gpu/drm/radeon/atombios_crtc.c
drivers/gpu/drm/radeon/evergreen_blit_kms.c
drivers/gpu/drm/radeon/r600.c
drivers/gpu/drm/radeon/r600_audio.c
drivers/gpu/drm/radeon/r600_blit_kms.c
drivers/gpu/drm/radeon/r600_cs.c
drivers/gpu/drm/radeon/r600_hdmi.c
drivers/gpu/drm/radeon/r600d.h
drivers/gpu/drm/radeon/radeon.h
drivers/gpu/drm/radeon/radeon_asic.h
drivers/gpu/drm/radeon/radeon_benchmark.c
drivers/gpu/drm/radeon/radeon_cp.c
drivers/gpu/drm/radeon/radeon_cs.c
drivers/gpu/drm/radeon/radeon_device.c
drivers/gpu/drm/radeon/radeon_display.c
drivers/gpu/drm/radeon/radeon_drv.c
drivers/gpu/drm/radeon/radeon_fb.c
drivers/gpu/drm/radeon/radeon_gart.c
drivers/gpu/drm/radeon/radeon_gem.c
drivers/gpu/drm/radeon/radeon_kms.c
drivers/gpu/drm/radeon/radeon_legacy_crtc.c
drivers/gpu/drm/radeon/radeon_mode.h
drivers/gpu/drm/radeon/radeon_object.c
drivers/gpu/drm/radeon/radeon_object.h
drivers/gpu/drm/radeon/radeon_ring.c
drivers/gpu/drm/radeon/radeon_test.c
drivers/gpu/drm/radeon/radeon_ttm.c
drivers/gpu/drm/radeon/rv770.c
drivers/gpu/drm/savage/savage_drv.c
drivers/gpu/drm/sis/sis_drv.c
drivers/gpu/drm/tdfx/tdfx_drv.c
drivers/gpu/drm/ttm/ttm_agp_backend.c
drivers/gpu/drm/ttm/ttm_bo.c
drivers/gpu/drm/ttm/ttm_page_alloc.c
drivers/gpu/drm/ttm/ttm_tt.c
drivers/gpu/drm/via/via_drv.c
drivers/gpu/drm/vmwgfx/vmwgfx_buffer.c
drivers/gpu/drm/vmwgfx/vmwgfx_drv.c
drivers/gpu/drm/vmwgfx/vmwgfx_ldu.c
drivers/misc/lis3lv02d/lis3lv02d.c
drivers/misc/lis3lv02d/lis3lv02d.h
drivers/misc/lis3lv02d/lis3lv02d_i2c.c
drivers/misc/lis3lv02d/lis3lv02d_spi.c
drivers/net/wireless/iwlegacy/iwl-3945-debugfs.c
drivers/net/wireless/iwlegacy/iwl-3945-fh.h
drivers/net/wireless/iwlegacy/iwl-3945-hw.h
drivers/net/wireless/iwlegacy/iwl-3945-rs.c
drivers/net/wireless/iwlegacy/iwl-3945.c
drivers/net/wireless/iwlegacy/iwl-3945.h
drivers/net/wireless/iwlegacy/iwl-4965-debugfs.h
drivers/net/wireless/iwlegacy/iwl-4965-eeprom.c
drivers/net/wireless/iwlegacy/iwl-4965-hw.h
drivers/net/wireless/iwlegacy/iwl-4965-led.c
drivers/net/wireless/iwlegacy/iwl-4965.c
drivers/net/wireless/iwlegacy/iwl3945-base.c
drivers/net/wireless/rtlwifi/rtl8192c/fw_common.c
drivers/net/wireless/rtlwifi/rtl8192c/fw_common.h
drivers/net/wireless/rtlwifi/rtl8192cu/rf.h
drivers/platform/x86/hp_accel.c
drivers/scsi/fcoe/fcoe_ctlr.c
drivers/watchdog/m54xx_wdt.c
deleting include/drm/i830_drm.h
include/drm/Kbuild
include/drm/drm.h
include/drm/drmP.h
include/drm/drm_crtc.h
include/drm/drm_hashtab.h
include/drm/drm_mm.h
include/drm/drm_mode.h
include/drm/drm_usb.h
include/drm/ttm/ttm_bo_driver.h
include/drm/ttm/ttm_page_alloc.h
include/linux/hid-roccat.h
include/linux/i2c-tegra.h
include/linux/i2c/atmel_mxt_ts.h
include/media/s5p_fimc.h
net/bluetooth/l2cap_core.c

I am pretty sure that git did not used to do this. Has anyone else seen
this?  I am running git version 1.7.4.1 from Debian unstable.
-- 
Cheers,
Stephen Rothwell                    sfr@canb.auug.org.au

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Re: new behaviour in git merge

[Jeff King]

On Thu, Feb 24, 2011 at 02:33:53PM +1100, Stephen Rothwell wrote:

> I am not sure when this started, but I think git has changed its behaviour
> when merging.   As you all know, I do a lot of merging of trees for
> linux-next each day.  Today I noticed that when I merge a tree, sometimes
> the timestamps are modified for files that are not modified on one side
> of the merge.  It is not consistent and it is not all the files that are
> modified on the HEAD side (relative to the merge-base).
>
> [...]
>
> I am pretty sure that git did not used to do this. Has anyone else seen
> this?  I am running git version 1.7.4.1 from Debian unstable.

I don't think any such change was intentional.  I couldn't reproduce
with a trivial example. Can you give the commit IDs of the two heads in
your example merge? I'd like to try bisecting if I can reproduce the
issue.

-Peff

Re: new behaviour in git merge

[Stephen Rothwell]

[-- Attachment #1: Type: text/plain, Size: 1139 bytes --]

Hi Jeff,

On Thu, 24 Feb 2011 03:15:53 -0500 Jeff King <peff@peff.net> wrote:
>
> I don't think any such change was intentional.  I couldn't reproduce

I was hoping that it was not intentional :-)

> with a trivial example. Can you give the commit IDs of the two heads in

I also tried a trivial example but failed to reproduce it.

> your example merge? I'd like to try bisecting if I can reproduce the
> issue.

In today's linux-next tree (available at
git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git),
commit ad11c1e8abca18872c2993b09b1abde418955b6c is just before the merge
and commit a2c06ee2fe5b48a71e697bae00c6e7195fc016b6 is what was merged.

I just did this in a copy of my tree:

	git reset --hard ad11c1e8abca18872c2993b09b1abde418955b6c
	sleep 90
	git merge a2c06ee2fe5b48a71e697bae00c6e7195fc016b6

A comparison of the ls -lR ouput before and after showed a lot of changed
modification times.

Several other merges showed the same problem.

Thanks for looking at this.
-- 
Cheers,
Stephen Rothwell                    sfr@canb.auug.org.au
http://www.canb.auug.org.au/~sfr/

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Re: new behaviour in git merge

[Jeff King]

[+cc Elijah Newren; this is a bug that bisects to one of your commits.
 The backstory is that during a merge, many unrelated files get
 unnecessarily re-written with the same content. Read on for details.]

On Thu, Feb 24, 2011 at 08:24:54PM +1100, Stephen Rothwell wrote:

> In today's linux-next tree (available at
> git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git),
> commit ad11c1e8abca18872c2993b09b1abde418955b6c is just before the merge
> and commit a2c06ee2fe5b48a71e697bae00c6e7195fc016b6 is what was merged.
> 
> I just did this in a copy of my tree:
> 
> 	git reset --hard ad11c1e8abca18872c2993b09b1abde418955b6c
> 	sleep 90
> 	git merge a2c06ee2fe5b48a71e697bae00c6e7195fc016b6
> 
> A comparison of the ls -lR ouput before and after showed a lot of changed
> modification times.
> 
> Several other merges showed the same problem.

Thanks for the reproduction recipe. I was able to bisect using this
script as my test:

-- >8 --
#!/bin/sh

stat() {
  git ls-files -z | xargs --null stat --format='%Y %n' | sort
}

cd linux-next &&
git reset --hard ad11c1e8abca18872c2993b09b1abde418955b6c &&
sleep 3 &&
stat >before &&
git merge a2c06ee2fe5b48a71e697bae00c6e7195fc016b6 &&
stat >after &&
comm -13 before after | cut -d' ' -f2 | sort >stat-diff &&
git diff-tree -r --name-only HEAD HEAD^ >tree-diff &&
comm -23 stat-diff tree-diff >extra-stats &&
if test -s extra-stats; then
  cat extra-stats
  echo FAIL
  exit 1
else
  echo OK
  exit 0
fi
-- 8< --

It bisects to 882fd11 (merge-recursive: Delay content merging for
renames, 2010-09-20). And indeed, looking further at the files that get
modified, they appear to be renames on one side of the merge, but not
touched on the other side. But rather than notice that there is nothing
to be done on them, we seem to update the index and write out the new
entries.

The patch below makes the problem go away in your test case, but also
introduces some test failures in t3509, so I'm sure there is something
else going on. I'm somewhat clueless about the merge code, so I'll defer
to Elijah, who wrote 882fd11, and see what he says.

-Peff

diff --git a/merge-recursive.c b/merge-recursive.c
index 0ca54bd..1dd643f 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -1083,7 +1083,8 @@ static int process_renames(struct merge_options *o,
 					b = ren1->pair->two;
 					a = &src_other;
 				}
-				update_stages_and_entry(ren1_dst, ren1->dst_entry, one, a, b, 1);
+				if (hashcmp(one->sha1, b->sha1))
+					update_stages_and_entry(ren1_dst, ren1->dst_entry, one, a, b, 1);
 				if (string_list_has_string(&o->current_directory_set, ren1_dst)) {
 					setup_rename_df_conflict_info(RENAME_NORMAL,
 								      ren1->pair,

[RFC PATCH 0/2] Fix unnecessary updates of files during merge

[Elijah Newren]

This patch series adds a simple testcase demonstrating the problem
reported by Stephen Rothwell, and a fix.  Unfortunately, there's a bug
with the fix (hence the RFC) that makes the relevant files racily clean
rather than clearly clean (i.e. 'git diff-files' will report these files
as modified when it shouldn't).

I'll try to figure out how to fix the second problem in the next few
days.  If anyone has some hints, I'm all ears.

Elijah Newren (2):
  t6022: New test checking for unnecessary updates of renamed+modified
    files
  merge-recursive: When we detect we can skip an update, actually skip
    it

 merge-recursive.c       |    7 +++++--
 t/t6022-merge-rename.sh |   32 ++++++++++++++++++++++++++++++++
 2 files changed, 37 insertions(+), 2 deletions(-)

-- 
1.7.4.1.23.g4865dd

[RFC PATCH 1/2] t6022: New test checking for unnecessary updates of renamed+modified files

[Elijah Newren]

Signed-off-by: Elijah Newren <newren@gmail.com>
---
 t/t6022-merge-rename.sh |   32 ++++++++++++++++++++++++++++++++
 1 files changed, 32 insertions(+), 0 deletions(-)

diff --git a/t/t6022-merge-rename.sh b/t/t6022-merge-rename.sh
index 1ed259d..71bfd22 100755
--- a/t/t6022-merge-rename.sh
+++ b/t/t6022-merge-rename.sh
@@ -609,4 +609,36 @@ test_expect_success 'check handling of differently renamed file with D/F conflic
 	! test -f original
 '
 
+test_expect_success 'setup avoid unnecessary update' '
+	git reset --hard &&
+	git checkout --orphan avoid-unnecessary-update &&
+	git rm -rf . &&
+	git clean -fdqx &&
+
+	printf "1\n2\n3\n4\n5\n6\n7\n8\n9\n10\n" >original &&
+	git add -A &&
+	git commit -m "Common commmit" &&
+
+	git mv original rename &&
+	echo 11 >>rename &&
+	git add -u &&
+	git commit -m "Renamed and modified" &&
+
+	git checkout -b other-branch HEAD~1 &&
+	echo "random content" >random-file &&
+	git add -A &&
+	git commit -m "Random, unrelated changes"
+'
+
+test_expect_failure 'avoid unnecessary update' '
+	git checkout -q avoid-unnecessary-update^0 &&
+	orig=$(stat --format="%Y" rename) &&
+	sleep 1 &&
+	git merge other-branch &&
+	new=$(stat --format="%Y" rename) &&
+	echo "Checking whether stat times are same: $orig vs $new" &&
+	test "$orig" == "$new" &&
+	git diff-files --exit-code # Is "rename" clean, or only racily clean?
+'
+
 test_done
-- 
1.7.4.1.23.g4865dd

[RFC PATCH 2/2] merge-recursive: When we detect we can skip an update, actually skip it

[Elijah Newren]

In 882fd11 (merge-recursive: Delay content merging for renames 2010-09-20),
the code that checked for whether we could skip updating a file in the
working directory (due to the merged version matching the current copy) was
moved into a separate function.  In order to defer the content merging, we
had to update the index with unmerged entries.  As part of the move, a bug
was introduced such that the message about skipping the update would be
printed (if GIT_MERGE_VERBOSITY was sufficiently high) but the file would
be updated in the working copy anyway.

When we detect that the file does not need to be updated in the working
copy, update the index to remove the unmerged entries and then return early
before updating the working copy.

STILL BROKEN: Unfortunately, this change leaves the index in a state where
the renamed file is only racily clean; a 'git diff-files' will report the
file as modified.

---
No Signed-off-by since it still doesn't work.

 merge-recursive.c |    7 +++++--
 1 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/merge-recursive.c b/merge-recursive.c
index 16c2dbe..94b818c 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -1274,9 +1274,12 @@ static int merge_content(struct merge_options *o,
 	}
 
 	if (mfi.clean && !df_conflict_remains &&
-	    sha_eq(mfi.sha, a_sha) && mfi.mode == a.mode)
+	    sha_eq(mfi.sha, a_sha) && mfi.mode == a.mode) {
 		output(o, 3, "Skipped %s (merged same as existing)", path);
-	else
+		add_cacheinfo(mfi.mode, mfi.sha, path,
+			      0, 0, ADD_CACHE_OK_TO_REPLACE);
+		return mfi.clean;
+	} else
 		output(o, 2, "Auto-merging %s", path);
 
 	if (!mfi.clean) {
-- 
1.7.4.1.23.g4865dd

Re: [RFC PATCH 0/2] Fix unnecessary updates of files during merge

[Elijah Newren]

Hi,

On Sat, Feb 26, 2011 at 11:34 AM, Elijah Newren <newren@gmail.com> wrote:
> This patch series adds a simple testcase demonstrating the problem
> reported by Stephen Rothwell, and a fix.  Unfortunately, there's a bug
> with the fix (hence the RFC) that makes the relevant files racily clean
> rather than clearly clean (i.e. 'git diff-files' will report these files
> as modified when it shouldn't).
>
> I'll try to figure out how to fix the second problem in the next few
> days.  If anyone has some hints, I'm all ears.

And, of course, I forgot to include the cc's in my send-email command.
 Sorry about that, Stephen and Jeff.  Adding you on this email, at
least.

> Elijah Newren (2):
>  t6022: New test checking for unnecessary updates of renamed+modified
>    files
>  merge-recursive: When we detect we can skip an update, actually skip
>    it
>
>  merge-recursive.c       |    7 +++++--
>  t/t6022-merge-rename.sh |   32 ++++++++++++++++++++++++++++++++
>  2 files changed, 37 insertions(+), 2 deletions(-)