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Diffstat (limited to 'hurd/io_path.mdwn')
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diff --git a/hurd/io_path.mdwn b/hurd/io_path.mdwn new file mode 100644 index 00000000..598ad967 --- /dev/null +++ b/hurd/io_path.mdwn @@ -0,0 +1,52 @@ +[[!meta copyright="Copyright © 2008, 2010 Free Software Foundation, Inc."]] + +[[!meta license="""[[!toggle id="license" text="GFDL 1.2+"]][[!toggleable +id="license" text="Permission is granted to copy, distribute and/or modify this +document under the terms of the GNU Free Documentation License, Version 1.2 or +any later version published by the Free Software Foundation; with no Invariant +Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license +is included in the section entitled [[GNU Free Documentation +License|/fdl]]."]]"""]] + +[[!meta title="I/O Path"]] + + +# read + + * [[glibc]]'s `read` is in `glibc/sysdeps/mach/hurd/read.c:__libc_read`. + + * That calls `glibc/hurd/fd-read.c:_hurd_fd_read()`. + + * That calls `__io_read`, which is an [[RPC]], i.e., that actually results + into the [[translator/ext2fs]] server calling + `hurd/libdiskfs/io-read.c:diskfs_S_io_read`. + + * That calls `_diskfs_rdwr_internal`, which calls + `hurd/libpager/pager-memcpy.c:pager_memcpy`, which usually basically just + tell the kernel to virtually project the memory object corresponding to the + file in the caller process's memory. No read is actually done. + + * Then, when the process actually reads the data, the kernel gets the user + page fault (`gnumach/i386/i386/trap.c:user_trap`), which calls `vm_fault`, + etc., until actually getting to `gnumach/vm/vm_fault/vm_fault_page` which + eventually calls `memory_object_data_request`, which is an [[RPC]], i.e., + that actually results into the [[translator/ext2fs]] server calling + `hurd/libpager/data-request.c:_pager_seqnos_memory_object_data_request`. + + * That calls `hurd/ext2fs/pager.c:pager_read_page`, which looks for where the + data is on the disk, and eventually calls + `hurd/libstore/rdwr.c:store_read`, which eventually calls `device_read`, + which is an [[RPC]], i.e., that actually gets into the kernel calling + `gnumach/linux/dev/glue/block.c:device_read`. + + * ext2fs eventually finishes the data_request() function, the kernel installs + the page into the process that got a fault. + + +# Documentation + + * In [*Linux kernel design patterns - part + 3*](http://lwn.net/Articles/336262/) (2009-06-22), Neil Brown gives a + nice overview of the related layering inside the Linux kernel, + including the VFS layer, page cache and directory entry cache + (dcache). |