Re: [Libguestfs] [PATCH] Use mount-options instead of mount to avoid implicit -o sync.

Subject: [PATCH] Use mount-options instead of mount to avoid implicit -o sync. guestfs_mount adds -o sync implicitly. This causes a very large performance problem for write-intensive programs (eg. virt-v2v). Document this as a "gotcha". Change the tests, guestfish, Sys::Guestfs::Lib, guestmount to use mount-options instead. (Note that this gotcha does not affect mount-ro). The source of the performance problem was first identified by Matthew Booth. --- fish/fish.c | 11 ++++-- fuse/guestmount.c | 11 ++++-- perl/lib/Sys/Guestfs/Lib.pm | 2 +- perl/t/060-readdir.t | 2 +- regressions/rhbz503169c10.sh | 2 +- regressions/rhbz503169c13.sh | 2 +- .../test-cancellation-upload-daemoncancels.sh | 2 +- regressions/test-remote.sh | 2 +- src/generator.ml | 34 ++++++++++---------- src/guestfs.pod | 9 +++++ test-tool/test-tool.c | 2 +- 11 files changed, 47 insertions(+), 32 deletions(-) diff --git a/fish/fish.c b/fish/fish.c index dd73af7..bc518da 100644 --- a/fish/fish.c +++ b/fish/fish.c @@ -474,10 +474,13 @@ mount_mps (struct mp *mp) if (mp) { mount_mps (mp->next); - if (!read_only) - r = guestfs_mount (g, mp->device, mp->mountpoint); - else - r = guestfs_mount_ro (g, mp->device, mp->mountpoint); + + /* Don't use guestfs_mount here because that will default to mount + * options -o sync,noatime. For more information, see guestfs(3) + * section "LIBGUESTFS GOTCHAS". + */ + const char *options = !read_only ? "" : "ro";

+ r = guestfs_mount_options (g, options, mp->device, mp->mountpoint); if (r == -1) exit (EXIT_FAILURE); } diff --git a/fuse/guestmount.c b/fuse/guestmount.c index c935493..cbd39f2 100644 --- a/fuse/guestmount.c +++ b/fuse/guestmount.c @@ -1160,10 +1160,13 @@ mount_mps (struct mp *mp) if (mp) { mount_mps (mp->next); - if (!read_only) - r = guestfs_mount (g, mp->device, mp->mountpoint); - else - r = guestfs_mount_ro (g, mp->device, mp->mountpoint); + + /* Don't use guestfs_mount here because that will default to mount + * options -o sync,noatime. For more information, see guestfs(3) + * section "LIBGUESTFS GOTCHAS". + */ + const char *options = !read_only ? "" : "ro";

+ r = guestfs_mount_options (g, options, mp->device, mp->mountpoint); if (r == -1) exit (EXIT_FAILURE); }