Pull Ceph updates from Sage Weil:
"A few groups of patches here. Alex has been hard at work improving
the RBD code, layout groundwork for understanding the new formats and
doing layering. Most of the infrastructure is now in place for the
final bits that will come with the next window.
There are a few changes to the data layout. Jim Schutt's patch fixes
some non-ideal CRUSH behavior, and a set of patches from me updates
the client to speak a newer version of the protocol and implement an
improved hashing strategy across storage nodes (when the server side
supports it too).
A pair of patches from Sam Lang fix the atomicity of open+create
operations. Several patches from Yan, Zheng fix various mds/client
issues that turned up during multi-mds torture tests.
A final set of patches expose file layouts via virtual xattrs, and
allow the policies to be set on directories via xattrs as well
(avoiding the awkward ioctl interface and providing a consistent
interface for both kernel mount and ceph-fuse users)."
* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/sage/ceph-client: (143 commits)
libceph: add support for HASHPSPOOL pool flag
libceph: update osd request/reply encoding
libceph: calculate placement based on the internal data types
ceph: update support for PGID64, PGPOOL3, OSDENC protocol features
ceph: update "ceph_features.h"
libceph: decode into cpu-native ceph_pg type
libceph: rename ceph_pg -> ceph_pg_v1
rbd: pass length, not op for osd completions
rbd: move rbd_osd_trivial_callback()
libceph: use a do..while loop in con_work()
libceph: use a flag to indicate a fault has occurred
libceph: separate non-locked fault handling
libceph: encapsulate connection backoff
libceph: eliminate sparse warnings
ceph: eliminate sparse warnings in fs code
rbd: eliminate sparse warnings
libceph: define connection flag helpers
rbd: normalize dout() calls
rbd: barriers are hard
rbd: ignore zero-length requests
...
The legacy behavior adds the pgid seed and pool together as the input for
CRUSH. That is problematic because each pool's PGs end up mapping to the
same OSDs: 1.5 == 2.4 == 3.3 == ...
Instead, if the HASHPSPOOL flag is set, we has the ps and pool together and
feed that into CRUSH. This ensures that two adjacent pools will map to
an independent pseudorandom set of OSDs.
Advertise our support for this via a protocol feature flag.
Signed-off-by: Sage Weil <sage@inktank.com>
Reviewed-by: Alex Elder <elder@inktank.com>
Use the new version of the encoding for osd requests and replies. In the
process, update the way we are tracking request ops and reply lengths and
results in the struct ceph_osd_request. Update the rbd and fs/ceph users
appropriately.
The main changes are:
- we keep pointers into the request memory for fields we need to update
each time the request is sent out over the wire
- we keep information about the result in an array in the request struct
where the users can easily get at it.
Signed-off-by: Sage Weil <sage@inktank.com>
Reviewed-by: Alex Elder <elder@inktank.com>
Instead of using the old ceph_object_layout struct, update our internal
ceph_calc_object_layout method to use the ceph_pg type. This allows us to
pass the full 32-bit precision of the pgid.seed to the callers. It also
allows some callers to avoid reaching into the request structures for the
struct ceph_object_layout fields.
Signed-off-by: Sage Weil <sage@inktank.com>
Reviewed-by: Alex Elder <elder@inktank.com>
Support (and require) the PGID64, PGPOOL3, and OSDENC protocol features.
These have been present in ceph.git since v0.42, Feb 2012. Require these
features to simplify support; nobody is running older userspace.
Note that the new request and reply encoding is still not in place, so the new
code is not yet functional.
Signed-off-by: Sage Weil <sage@inktank.com>
Reviewed-by: Alex Elder <elder@inktank.com>
Always decode data into our cpu-native ceph_pg type that has the correct
field widths. Limit any remaining uses of ceph_pg_v1 to dealing with the
legacy protocol.
Signed-off-by: Sage Weil <sage@inktank.com>
Reviewed-by: Alex Elder <elder@inktank.com>
Rename the old version this type to distinguish it from the new version.
Signed-off-by: Sage Weil <sage@inktank.com>
Reviewed-by: Alex Elder <elder@inktank.com>
Pull user namespace and namespace infrastructure changes from Eric W Biederman:
"This set of changes starts with a few small enhnacements to the user
namespace. reboot support, allowing more arbitrary mappings, and
support for mounting devpts, ramfs, tmpfs, and mqueuefs as just the
user namespace root.
I do my best to document that if you care about limiting your
unprivileged users that when you have the user namespace support
enabled you will need to enable memory control groups.
There is a minor bug fix to prevent overflowing the stack if someone
creates way too many user namespaces.
The bulk of the changes are a continuation of the kuid/kgid push down
work through the filesystems. These changes make using uids and gids
typesafe which ensures that these filesystems are safe to use when
multiple user namespaces are in use. The filesystems converted for
3.9 are ceph, 9p, afs, ocfs2, gfs2, ncpfs, nfs, nfsd, and cifs. The
changes for these filesystems were a little more involved so I split
the changes into smaller hopefully obviously correct changes.
XFS is the only filesystem that remains. I was hoping I could get
that in this release so that user namespace support would be enabled
with an allyesconfig or an allmodconfig but it looks like the xfs
changes need another couple of days before it they are ready."
* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace: (93 commits)
cifs: Enable building with user namespaces enabled.
cifs: Convert struct cifs_ses to use a kuid_t and a kgid_t
cifs: Convert struct cifs_sb_info to use kuids and kgids
cifs: Modify struct smb_vol to use kuids and kgids
cifs: Convert struct cifsFileInfo to use a kuid
cifs: Convert struct cifs_fattr to use kuid and kgids
cifs: Convert struct tcon_link to use a kuid.
cifs: Modify struct cifs_unix_set_info_args to hold a kuid_t and a kgid_t
cifs: Convert from a kuid before printing current_fsuid
cifs: Use kuids and kgids SID to uid/gid mapping
cifs: Pass GLOBAL_ROOT_UID and GLOBAL_ROOT_GID to keyring_alloc
cifs: Use BUILD_BUG_ON to validate uids and gids are the same size
cifs: Override unmappable incoming uids and gids
nfsd: Enable building with user namespaces enabled.
nfsd: Properly compare and initialize kuids and kgids
nfsd: Store ex_anon_uid and ex_anon_gid as kuids and kgids
nfsd: Modify nfsd4_cb_sec to use kuids and kgids
nfsd: Handle kuids and kgids in the nfs4acl to posix_acl conversion
nfsd: Convert nfsxdr to use kuids and kgids
nfsd: Convert nfs3xdr to use kuids and kgids
...
This just converts a manually-implemented loop into a do..while loop
in con_work(). It also moves handling of EAGAIN inside the blocks
where it's already been determined an error code was returned.
Also update a few dout() calls near the affected code for
consistency.
Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
This just rearranges the logic in con_work() a little bit so that a
flag is used to indicate a fault has occurred. This allows both the
fault and non-fault case to be handled the same way and avoids a
couple of nearly consecutive gotos.
Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
An error occurring on a ceph connection is treated as a fault,
causing the connection to be reset. The initial part of this fault
handling has to be done while holding the connection mutex, but
it must then be dropped for the last part.
Separate the part of this fault handling that executes without the
lock into its own function, con_fault_finish(). Move the call to
this new function, as well as call that drops the connection mutex,
into ceph_fault(). Rename that function con_fault() to reflect that
it's only handling the connection part of the fault handling.
The motivation for this was a warning from sparse about the locking
being done here. Rearranging things this way keeps all the mutex
manipulation within ceph_fault(), and this stops sparse from
complaining.
This partially resolves:
http://tracker.ceph.com/issues/4184
Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
Collect the code that tests for and implements a backoff delay for a
ceph connection into a new function, ceph_backoff().
Make the debug output messages in that part of the code report
things consistently by reporting a message in the socket closed
case, and by making the one for PREOPEN state report the connection
pointer like the rest.
Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
Eliminate most of the problems in the libceph code that cause sparse
to issue warnings.
- Convert functions that are never referenced externally to have
static scope.
- Pass NULL rather than 0 for a pointer argument in one spot in
ceph_monc_delete_snapid()
This partially resolves:
http://tracker.ceph.com/issues/4184
Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
Define and use functions that encapsulate operations performed on
a connection's flags.
This resolves:
http://tracker.ceph.com/issues/4234
Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
The return values provided for ceph_copy_to_page_vector() and
ceph_copy_from_page_vector() serve no purpose, so get rid of them.
Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
The functions used for working with ceph page vectors are defined
with char pointers, but they're really intended to operate on
untyped data. Change the types of these function parameters
to (void *) to reflect this.
(Note that the functions now assume void pointer arithmetic works
like arithmetic on char pointers.)
Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
Add support for CEPH_OSD_OP_STAT operations in the osd client
and in rbd.
This operation sends no data to the osd; everything required is
encoded in identity of the target object.
The result will be ENOENT if the object doesn't exist. If it does
exist and no other error occurs the server returns the size and last
modification time of the target object as output data (in little
endian format). The size is a 64 bit unsigned and the time is
ceph_timespec structure (two unsigned 32-bit integers, representing
a seconds and nanoseconds value).
This resolves:
http://tracker.ceph.com/issues/4007
Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
Simplify the way the data length recorded in a message header is
calculated in ceph_osdc_build_request().
Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
In osd_req_encode_op() there are a few cases that handle osd
opcodes that are never used in the kernel. The presence of
this code gives the impression it's correct (which really can't
be assumed), and may impose some unnecessary restrictions on
some upcoming refactoring of this code.
So delete this effectively dead code, and report uses of the
previously handled cases as unsupported.
Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
If osd_req_encode_op() is given any opcode it doesn't recognize
it reports an error.
This patch fleshes out that routine to distinguish between
well-defined but unsupported values and values that are simply
bogus.
This and the next commit are related to:
http://tracker.ceph.com/issues/4126
Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
Update ceph_osd_op_name() to include the newly-added definitions in
"rados.h", and to match its counterpart in the user space code.
Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
Add the definition of ceph_osd_state_name(), to match its
counterpart in user space.
Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
There are no actual users of ceph_osdc_wait_event(). This would
have been one-shot events, but we no longer support those so just
get rid of this function.
Since this leaves nothing else that waits for the completion of an
event, we can get rid of the completion in a struct ceph_osd_event.
Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
There is only one caller of ceph_osdc_create_event(), and it
provides 0 as its "one_shot" argument. Get rid of that argument and
just use 0 in its place.
Replace the code in handle_watch_notify() that executes if one_shot
is nonzero in the event with a BUG_ON() call.
While modifying "osd_client.c", give handle_watch_notify() static
scope.
Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
There is no caller of ceph_calc_raw_layout() outside of libceph, so
there's no need to export from the module.
Furthermore, there is only one caller, in calc_layout(), and it
is not much more than a simple wrapper for that function.
So get rid of ceph_calc_raw_layout() and embed it instead within
calc_layout().
While touching "osd_client.c", get rid of the unnecessary forward
declaration of __send_request().
Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
The only callers of ceph_osdc_init() and ceph_osdc_stop()
ceph_create_client() and ceph_destroy_client() (respectively)
and they are in the same kernel module as those two functions.
There's therefore no need to export those interfaces, so don't.
Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
Two of the three callers of the osd client's send_queued() function
already hold the osd client mutex and drop it before the call.
Change send_queued() so it assumes the caller holds the mutex, and
update all callers accordingly. Rename it __send_queued() to match
the convention used elsewhere in the file with respect to the lock.
Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
The "num_reply" parameter to ceph_osdc_new_request() is never
used inside that function, so get rid of it.
Note that ceph_sync_write() passes 2 for that argument, while all
other callers pass 1. It doesn't matter, but perhaps someone should
verify this doesn't indicate a problem.
Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
There is only one caller of ceph_osdc_writepages(), and it always
passes 0 as its "flags" argument. Get rid of that argument and
replace its use in ceph_osdc_writepages() with 0.
Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
There is only one caller of ceph_osdc_writepages(), and it always
passes 0 as its "dosync" argument. Get rid of that argument and
replace its use in ceph_osdc_writepages() with 0.
Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
There is only one caller of ceph_osdc_writepages(), and it always
passes the value true as its "nofail" argument. Get rid of that
argument and replace its use in ceph_osdc_writepages() with the
constant value true.
This and a number of cleanup patches that follow resolve:
http://tracker.ceph.com/issues/4126
Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
There is a check in the completion path for osd requests that
ensures the number of pages allocated is enough to hold the amount
of incoming data expected.
For bio requests coming from rbd the "number of pages" is not really
meaningful (although total length would be). So stop requiring that
nr_pages be supplied for bio requests. This is done by checking
whether the pages pointer is null before checking the value of
nr_pages.
Note that this value is passed on to the messenger, but there it's
only used for debugging--it's never used for validation.
While here, change another spot that used r_pages in a debug message
inappropriately, and also invalidate the r_con_filling_msg pointer
after dropping a reference to it.
This resolves:
http://tracker.ceph.com/issues/3875
Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
Currently, if the OSD client finds an osd request has had a bio list
attached to it, it drops a reference to it (or rather, to the first
entry on that list) when the request is released.
The code that added that reference (i.e., the rbd client) is
therefore required to take an extra reference to that first bio
structure.
The osd client doesn't really do anything with the bio pointer other
than transfer it from the osd request structure to outgoing (for
writes) and ingoing (for reads) messages. So it really isn't the
right place to be taking or dropping references.
Furthermore, the rbd client already holds references to all bio
structures it passes to the osd client, and holds them until the
request is completed. So there's no need for this extra reference
whatsoever.
So remove the bio_put() call in ceph_osdc_release_request(), as
well as its matching bio_get() call in rbd_osd_req_create().
This change could lead to a crash if old libceph.ko was used with
new rbd.ko. Add a compatibility check at rbd initialization time to
avoid this possibilty.
This resolves:
http://tracker.ceph.com/issues/3798 and
http://tracker.ceph.com/issues/3799
Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
An upcoming change implements semantic change that could lead to
a crash if an old version of the libceph kernel module is used with
a new version of the rbd kernel module.
In order to preclude that possibility, this adds a compatibilty
check interface. If this interface doesn't exist, the modules are
obviously not compatible. But if it does exist, this provides a way
of letting the caller know whether it will operate properly with
this libceph module.
Perhaps confusingly, it returns false right now. The semantic
change mentioned above will make it return true.
This resolves:
http://tracker.ceph.com/issues/3800
Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
The ceph messenger has a few spots that are only used when
bio messages are supported, and that's only when CONFIG_BLOCK
is defined. This surrounds a couple of spots with #ifdef's
that would cause a problem if CONFIG_BLOCK were not present
in the kernel configuration.
This resolves:
http://tracker.ceph.com/issues/3976
Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
Today ceph opens tcp sockets from a delayed work callback. Delayed
work happens from kernel threads which are always in the initial
network namespace. Therefore fail early if someone attempts
to mount a ceph filesystem from something other than the initial
network namespace.
Cc: Sage Weil <sage@inktank.com>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
The variable "str" is used as both the source and destination in
function snprintf(), which is undefined behavior based on C11. The
original description in C11 is:
"If copying takes place between objects that
overlap, the behavior is undefined."
And, the function of ceph_osdmap_state_str() is to return the osdmap
state, so it should return "doesn't exist" when all the conditions
are not satisfied. I fix it in this patch.
[elder@inktank.com: shortened the commit message]
Signed-off-by: Cong Ding <dinggnu@gmail.com>
Reviewed-by: Alex Elder <elder@inktank.com>
Both ceph_osdc_alloc_request() and ceph_osdc_build_request() are
provided an array of ceph osd request operations. Rather than just
passing the number of operations in the array, the caller is
required append an additional zeroed operation structure to signal
the end of the array.
All callers know the number of operations at the time these
functions are called, so drop the silly zero entry and supply that
number directly. As a result, get_num_ops() is no longer needed.
This also means that ceph_osdc_alloc_request() never uses its ops
argument, so that can be dropped.
Also rbd_create_rw_ops() no longer needs to add one to reserve room
for the additional op.
Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
Only one of the two callers of ceph_osdc_alloc_request() provides
page or bio data for its payload. And essentially all that function
was doing with those arguments was assigning them to fields in the
osd request structure.
Simplify ceph_osdc_alloc_request() by having the caller take care of
making those assignments
Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
The only thing ceph_osdc_alloc_request() really does with the
flags value it is passed is assign it to the newly-created
osd request structure. Do that in the caller instead.
Both callers subsequently call ceph_osdc_build_request(), so have
that function (instead of ceph_osdc_alloc_request()) issue a warning
if a request comes through with neither the read nor write flags set.
Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
The osdc parameter to ceph_calc_raw_layout() is not used, so get rid
of it. Consequently, the corresponding parameter in calc_layout()
becomes unused, so get rid of that as well.
Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
A snapshot id must be provided to ceph_calc_raw_layout() even though
it is not needed at all for calculating the layout.
Where the snapshot id *is* needed is when building the request
message for an osd operation.
Drop the snapid parameter from ceph_calc_raw_layout() and pass
that value instead in ceph_osdc_build_request().
Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
ceph_calc_file_object_mapping() takes (among other things) a "file"
offset and length, and based on the layout, determines the object
number ("bno") backing the affected portion of the file's data and
the offset into that object where the desired range begins. It also
computes the size that should be used for the request--either the
amount requested or something less if that would exceed the end of
the object.
This patch changes the input length parameter in this function so it
is used only for input. That is, the argument will be passed by
value rather than by address, so the value provided won't get
updated by the function.
The value would only get updated if the length would surpass the
current object, and in that case the value it got updated to would
be exactly that returned in *oxlen.
Only one of the two callers is affected by this change. Update
ceph_calc_raw_layout() so it records any updated value.
Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
The len argument to ceph_osdc_build_request() is set up to be
passed by address, but that function never updates its value
so there's no need to do this. Tighten up the interface by
passing the length directly.
Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
Since every osd message is now prepared to include trailing data,
there's no need to check ahead of time whether any operations will
make use of the trail portion of the message.
We can drop the second argument to get_num_ops(), and as a result we
can also get rid of op_needs_trail() which is no longer used.
Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
An osd request structure contains an optional trail portion, which
if present will contain data to be passed in the payload portion of
the message containing the request. The trail field is a
ceph_pagelist pointer, and if null it indicates there is no trail.
A ceph_pagelist structure contains a length field, and it can
legitimately hold value 0. Make use of this to change the
interpretation of the "trail" of an osd request so that every osd
request has trailing data, it just might have length 0.
This means we change the r_trail field in a ceph_osd_request
structure from a pointer to a structure that is always initialized.
Note that in ceph_osdc_start_request(), the trail pointer (or now
address of that structure) is assigned to a ceph message's trail
field. Here's why that's still OK (looking at net/ceph/messenger.c):
- What would have resulted in a null pointer previously will now
refer to a 0-length page list. That message trail pointer
is used in two functions, write_partial_msg_pages() and
out_msg_pos_next().
- In write_partial_msg_pages(), a null page list pointer is
handled the same as a message with 0-length trail, and both
result in a "in_trail" variable set to false. The trail
pointer is only used if in_trail is true.
- The only other place the message trail pointer is used is
out_msg_pos_next(). That function is only called by
write_partial_msg_pages() and only touches the trail pointer
if the in_trail value it is passed is true.
Therefore a null ceph_msg->trail pointer is equivalent to a non-null
pointer referring to a 0-length page list structure.
Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
The last two parameters to ceph_osd_build_request() describe the
object id, but the values passed always come from the osd request
structure whose address is also provided. Get rid of those last
two parameters.
Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
Reformat __reset_osd() into three distinct blocks of code
handling the three return cases.
Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
This saves us some cycles, but does not affect the placement result at
all.
This corresponds to ceph.git commit 4abb53d4f.
Signed-off-by: Sage Weil <sage@inktank.com>
Linus Torvalds