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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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This commit is contained in:
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
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
nsh> ls /mnt/unionfs/adir
/mnt/unionfs/adir:
nsh> ls /mnt/unionfs
/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/
adirfile.txt
bsubdir/
bdirfile.txt
.
adir/ exists in both file system 1 and file system 2. Above you are
looking at the merged content. The unified directory listing is showing
files from both file systems in their respective adir/ subdirectory.
The file adirfile.txt exists in both file system 1 and file system 2 but
the version if file system 2 is occluded by the version in file system 1.
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
The unified directory listing is showing files from both file systems in
their respective offset adir/ subdirectories. The file adirfile.txt
exists in both file system 1 and file system 2 but the version if file
system 2 is occluded by the version in file system 1. The only way
that you can which are looking at is by cat'ing the file:
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
name on file system 2. bdirfile.txt, however, only exists on file
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
You can see the files in the two file systems before they were unified at