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Extend apps/examples/unionfs so it is includes a root offset on one of the unified file sysems

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Gregory Nutt 2015-06-21 12:21:54 -06:00
parent 0e98c595c2
commit 1afba254b6
1 changed files with 45 additions and 12 deletions
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57
configs/sim/README.txt
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@ -712,30 +712,63 @@ unionfs
nsh> unionfs nsh> unionfs
Mounting ROMFS file system 1 at target=/mnt/a with source=/dev/ram4 Mounting ROMFS file system 1 at target=/mnt/a with source=/dev/ram4
Mounting ROMFS file system 2 at target=/mnt/b with source=/dev/ram5 Mounting ROMFS file system 2 at target=/mnt/b with source=/dev/ram5
nsh> ls /mnt/unionfs/adir nsh> ls /mnt/unionfs
/mnt/unionfs/adir: /mnt/unionfs:
.
afile.txt
offset/
When unionfs was created, file system was joined with and offset called
offset". Therefore, all of the file system 2 root contents will appear
to reside under a directory called offset/ (although there is no
directory called offset/ on file system 2). Fie system 1 on the other
hand does have an actual directory called offset/. If we list the
contents of the offset/ directory in the unified file system, we see
he merged content of the file system 1 offset/ directory and the file
system 2 root directory:
nsh> cat /mnt/unionfs/afile.txt
This is a file in the root directory on file system 1
nsh> ls /mnt/unionfs/offset
/mnt/unionfs/offset:
afile.txt
.
adir/
bfile.txt
bdir/
nsh> cat /mnt/unionfs/offset/afile.txt
This is a file in the offset/ directory on file system 1
nsh> cat /mnt/unionfs/offset/bfile.txt
This is another file in the root directory on file system 2
The directory offset/adir exists on file system 1 and the directory\
adir/ exists on file system 2. You can see that these also overlap:
nsh> ls /mnt/unionfs/offset/adir
/mnt/unionfs/offset/adir:
.. ..
asubdir/ asubdir/
adirfile.txt adirfile.txt
bsubdir/ bsubdir/
bdirfile.txt bdirfile.txt
.
adir/ exists in both file system 1 and file system 2. Above you are The unified directory listing is showing files from both file systems in
looking at the merged content. The unified directory listing is showing their respective offset adir/ subdirectories. The file adirfile.txt
files from both file systems in their respective adir/ subdirectory. exists in both file system 1 and file system 2 but the version if file
The file adirfile.txt exists in both file system 1 and file system 2 but system 2 is occluded by the version in file system 1. The only way
the version if file system 2 is occluded by the version in file system 1. that you can which are looking at is by cat'ing the file:
The only way that you can which are looking at is by cat'ing the file:
nsh> cat /mnt/unionfs/adir/adirfile.txt
This is a file in directory adir on file system 1
nsh> cat /mnt/unionfs/offset/adir/adirfile.txt
This is a file in directory offset/adir on file system 1
The file on file system 1 has correctly occluded the file with the same The file on file system 1 has correctly occluded the file with the same
name on file system 2. bdirfile.txt, however, only exists on file name on file system 2. bdirfile.txt, however, only exists on file
system 2, so it is not occluded: system 2, so it is not occluded:
nsh> cat /mnt/unionfs/adir/bdirfile.txt nsh> cat /mnt/unionfs/offset/adir/bdirfile.txt
This is another file in directory adir on file system 2 This is another file in directory adir on file system 2
You can see the files in the two file systems before they were unified at You can see the files in the two file systems before they were unified at