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authorThomas Schwinge <tschwing@ikr.uni-stuttgart.de>2008-07-11 10:52:23 +0200
committerThomas Schwinge <tschwing@ikr.uni-stuttgart.de>2008-07-11 10:52:23 +0200
commit13cb1fb472bc55edabe9262ece9b5290488216a3 (patch)
tree64ecfdd43da3799153d73414a3d5bfaaf8de541d
parent6c5f1cbc23e826a1653730036ed9acfd50b27c8d (diff)
New file [[hurd/io_path]], based on an email by Samuel Thibault, bug-hurd, 2008-03-27.
-rw-r--r--hurd.mdwn1
-rw-r--r--hurd/io_path.mdwn37
2 files changed, 38 insertions, 0 deletions
diff --git a/hurd.mdwn b/hurd.mdwn
index 1edf4d55..ff1f2916 100644
--- a/hurd.mdwn
+++ b/hurd.mdwn
@@ -64,5 +64,6 @@
* [[libstore]]
* [[libchannel]]
* [[libhello_example]] -- Hurd library example
+* [[IO_Path]]
* [[Debugging]]
* [Hurd Sourcecode Reference](http://www.htu.tugraz.at/~past/hurd/global/): Searchable and browsable index of the code.
diff --git a/hurd/io_path.mdwn b/hurd/io_path.mdwn
new file mode 100644
index 00000000..96e6aa58
--- /dev/null
+++ b/hurd/io_path.mdwn
@@ -0,0 +1,37 @@
+[[meta copyright="Copyright © 2008 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]]."]]"""]]
+
+# 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`.