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Merge pull request #1309 from trapexit/root-nodeid

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Root nodeid
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51
README.md
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@ -682,21 +682,13 @@ is empty is opened for writing.
In theory this flag should not be exposed to the end user. It is a
low-level FUSE flag which indicates whether or not the kernel can send
certain kinds of messages to it for the purposes of using with
NFS. mergerfs does support these messages but due to a possible bug in
the Linux kernel this option needs to be configurable. As it turns out
at least certain versions of NFS can still work when disabled and no
longer triggers the bug.
While it may be safe to default this setting to `false` in an
abundance of caution it is being left enabled by default.
NFS. mergerfs does support these messages but due bugs and quirks
found in the kernel and mergerfs this option is provided just in case
it is needed for debugging.
Given that this flag is set when the FUSE connection is first
initiated it is not possible to change during run time.
See [Kernel Issues &
Bugs](https://github.com/trapexit/mergerfs/wiki/Kernel-Issues-&-Bugs)
for more details.
# FUNCTIONS, CATEGORIES and POLICIES
@ -2047,17 +2039,19 @@ remote filesystem on Unix/POSIX systems. Due to how NFS works there
are some settings which need to be set in order for mergerfs to work
with it.
It should be noted that NFS and FUSE (the technology mergerfs uses)
do not work perfectly with one another due to certain design
choices in FUSE (and mergerfs.) Due to these issues it is
generally recommended to use SMB when possible till situations
change. That said issues should still be reported. NFS is not really
recommended but it isn't unsupported.
It should be noted that NFS and FUSE (the technology mergerfs uses) do
not work perfectly with one another due to certain design choices in
FUSE (and mergerfs.) Due to these issues it is generally recommended
to use SMB when possible till situations change. That said mergerfs
should generally work as an export of NFS and issues discovered should
still be reported.
To ensure compatibility between mergerfs and NFS use the following
settings.
mergerfs settings:
* noforget
* inodecalc=path-hash
* export-support=false (only available in v2.40.0 and above)
NFS export settings:
* fsid=UUID
@ -2080,32 +2074,17 @@ calculation algorithm then it is possible that if you changed a file
or updated a directory the file mergerfs will use will be on a
different branch and therefore the inode would change. This isn't an
ideal solution and others are being considered but it works for most
situations. It might be possible to leave the default value of
`hybrid-hash` if `export-support=false` but it hasn't been fully
tested yet.
`export-support=false` is a low-level FUSE option that is needed as a
workaround to a Linux kernel bug. Technically this option should be
set to `true` when expecting to use mergerfs with NFS but it turns out
that at least some versions of NFS work when not enabled. At the
moment it is unclear if this has any negative side effects but when
disabled NFS appears to work alright and the kernel no longer sends
invalid requests. When the issue is resolved in the kernel these docs
will be updated with appropriate details.
Also see [Kernel Issues &
Bugs](https://github.com/trapexit/mergerfs/wiki/Kernel-Issues-&-Bugs)
for more details.
situations.
`fsid=UUID` is needed because FUSE filesystems don't have different
`st_dev` values which can cause issues when exporting. The easiest
thing to do is set each mergerfs export `fsid` to some random
value. An easy way to generate a random value is to use the command
line tool `uuidgen` or through a website such as
line tool `uuid` or `uuidgen` or through a website such as
[uuidgenerator.net](https://www.uuidgenerator.net/).
`no_root_squash` is not strictly necessary but can lead to confusing
permission and ownership issues.
permission and ownership issues if root squashing is enabled.
## SMB / CIFS

11
libfuse/lib/fuse.c
View File

@ -1375,7 +1375,7 @@ set_path_info(struct fuse *f,
return -ENOMEM;
e->ino = node->nodeid;
e->generation = f->nodeid_gen.generation;
e->generation = ((e->ino == FUSE_ROOT_ID) ? 0 : f->nodeid_gen.generation);
pthread_mutex_lock(&f->lock);
update_stat(node,&e->attr);
@ -1386,6 +1386,15 @@ set_path_info(struct fuse *f,
return 0;
}
/*
lookup requests only come in for FUSE_ROOT_ID when a "parent of
child of root node" request is made. This can happen when using
EXPORT_SUPPORT=true and a file handle is used to keep a reference to
a node which has been forgotten. Mostly a NFS concern but not
excluslively. Root node always has a nodeid of 1 and generation of
0. To ensure this set_path_info() explicitly ensures the root id has
a generation of 0.
*/
static
int
lookup_path(struct fuse *f,

5
libfuse/lib/fuse_lowlevel.c
View File

@ -294,6 +294,11 @@ fuse_reply_entry(fuse_req_t req,
fill_entry(&arg, e);
#ifdef NDEBUG
// TODO: Add checks for cases where a node could be marked bad by
// the kernel.
#endif
return send_reply_ok(req, &arg, size);
}

56
man/mergerfs.1
View File

@ -115,7 +115,7 @@ start with one of the following option sets.
\f[C]mergerfs -o cache.files=partial,dropcacheonclose=true,category.create=mfs /mnt/hdd0:/mnt/hdd1 /media\f[R]
.SS /etc/fstab
.PP
\f[C]/mnt/hdd0:/mnt/hdd1 /media fuse.mergerfs cache.files=partial,dropcacheonclose=true,category.create=mfs 0 0\f[R]
\f[C]/mnt/hdd0:/mnt/hdd1 /media mergerfs cache.files=partial,dropcacheonclose=true,category.create=mfs 0 0\f[R]
.SS systemd mount
.PP
https://github.com/trapexit/mergerfs/wiki/systemd
@ -516,8 +516,8 @@ tools use \f[B]/etc/fstab\f[R].
.IP
.nf
\f[C]
# <file system> <mount point> <type> <options> <dump> <pass>
/mnt/hdd*:/mnt/ssd /media fuse.mergerfs minfreespace=16G 0 0
# <file system> <mount point> <type> <options> <dump> <pass>
/mnt/hdd*:/mnt/ssd /media mergerfs minfreespace=16G 0 0
\f[R]
.fi
.PP
@ -847,20 +847,12 @@ In theory this flag should not be exposed to the end user.
It is a low-level FUSE flag which indicates whether or not the kernel
can send certain kinds of messages to it for the purposes of using with
NFS.
mergerfs does support these messages but due to a possible bug in the
Linux kernel this option needs to be configurable.
As it turns out at least certain versions of NFS can still work when
disabled and no longer triggers the bug.
.PP
While it may be safe to default this setting to \f[C]false\f[R] in an
abundance of caution it is being left enabled by default.
mergerfs does support these messages but due bugs and quirks found in
the kernel and mergerfs this option is provided just in case it is
needed for debugging.
.PP
Given that this flag is set when the FUSE connection is first initiated
it is not possible to change during run time.
.PP
See Kernel Issues &
Bugs (https://github.com/trapexit/mergerfs/wiki/Kernel-Issues-&-Bugs)
for more details.
.SH FUNCTIONS, CATEGORIES and POLICIES
.PP
The POSIX filesystem API is made up of a number of functions.
@ -1577,8 +1569,8 @@ apply those before mounting the new version.
\f[C]
$ sudo mount /mnt/mergerfs
$ mount | grep mergerfs
media on /mnt/mergerfs type fuse.mergerfs (rw,relatime,user_id=0,group_id=0,default_permissions,allow_other)
media on /mnt/mergerfs type fuse.mergerfs (rw,relatime,user_id=0,group_id=0,default_permissions,allow_other)
media on /mnt/mergerfs type mergerfs (rw,relatime,user_id=0,group_id=0,default_permissions,allow_other)
media on /mnt/mergerfs type mergerfs (rw,relatime,user_id=0,group_id=0,default_permissions,allow_other)
\f[R]
.fi
.PP
@ -2588,11 +2580,13 @@ It should be noted that NFS and FUSE (the technology mergerfs uses) do
not work perfectly with one another due to certain design choices in
FUSE (and mergerfs.) Due to these issues it is generally recommended to
use SMB when possible till situations change.
That said issues should still be reported.
NFS is not really recommended but it isn\[cq]t unsupported.
That said mergerfs should generally work as an export of NFS and issues
discovered should still be reported.
.PP
mergerfs settings: * noforget * inodecalc=path-hash *
export-support=false (only available in v2.40.0 and above)
To ensure compatibility between mergerfs and NFS use the following
settings.
.PP
mergerfs settings: * noforget * inodecalc=path-hash
.PP
NFS export settings: * fsid=UUID * no_root_squash
.PP
@ -2618,35 +2612,17 @@ mergerfs will use will be on a different branch and therefore the inode
would change.
This isn\[cq]t an ideal solution and others are being considered but it
works for most situations.
It might be possible to leave the default value of \f[C]hybrid-hash\f[R]
if \f[C]export-support=false\f[R] but it hasn\[cq]t been fully tested
yet.
.PP
\f[C]export-support=false\f[R] is a low-level FUSE option that is needed
as a workaround to a Linux kernel bug.
Technically this option should be set to \f[C]true\f[R] when expecting
to use mergerfs with NFS but it turns out that at least some versions of
NFS work when not enabled.
At the moment it is unclear if this has any negative side effects but
when disabled NFS appears to work alright and the kernel no longer sends
invalid requests.
When the issue is resolved in the kernel these docs will be updated with
appropriate details.
.PP
Also see Kernel Issues &
Bugs (https://github.com/trapexit/mergerfs/wiki/Kernel-Issues-&-Bugs)
for more details.
.PP
\f[C]fsid=UUID\f[R] is needed because FUSE filesystems don\[cq]t have
different \f[C]st_dev\f[R] values which can cause issues when exporting.
The easiest thing to do is set each mergerfs export \f[C]fsid\f[R] to
some random value.
An easy way to generate a random value is to use the command line tool
\f[C]uuidgen\f[R] or through a website such as
\f[C]uuid\f[R] or \f[C]uuidgen\f[R] or through a website such as
uuidgenerator.net (https://www.uuidgenerator.net/).
.PP
\f[C]no_root_squash\f[R] is not strictly necessary but can lead to
confusing permission and ownership issues.
confusing permission and ownership issues if root squashing is enabled.
.SS SMB / CIFS
.PP
SMB (https://en.wikipedia.org/wiki/Server_Message_Block) is a protocol