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This has been done because a slow client attack is possible if the
async thread pool is used. The scenario is:
Client does a request for a file and then slowly receives the file one
byte at a time. This will eventually fill the async thread pool with blocking
sendfile operations and thus starving the vm of all file operations.
If you still want to use the async threads pool for sendfile an option to
enable it has been introduced.
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* sv/file-osync/OTP-11498:
Add sync option to file:open/2
Conflicts:
erts/preloaded/ebin/prim_file.beam
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The sync option adds the POSIX O_SYNC flag to the open system call on
platforms that support the flag or its equivalent, e.g.,
FILE_FLAG_WRITE_THROUGH on Windows. For platforms that don't support it,
file:open/2 returns {error, enotsup} if the sync option is passed in.
The semantics of O_SYNC are platform-specific. For example, not all
platforms guarantee that all file metadata are written to the disk along
with the file data when the flag is in effect. This issue is noted in the
documentation this commit adds for the sync option.
Add a test for the sync option. Note however that the underlying OS
semantics for O_SYNC can't be tested automatically in any practical way, so
the test assumes the OS does the right thing with the flag when
present. For manual verification, dtruss on OS X and strace on Linux were
both run against beam processes to watch calls to open(), and file:open/2
was called in Erlang shells to open files for writing, both with and
without the sync option. Both the dtruss output and the strace output
showed that the O_SYNC flag was present in the open() calls when sync was
specified and was clear when sync was not specified.
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* hb/file_name_type/OTP-10852:
Introduce new type file:name_all()
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The recommended type for filenames is a list of characters (which
may be Unicode characters greater than 255). Change the
file:filename() to reflect that.
For the filename module we still need a type that can be either
a string or a binary, so we need to introduce the type
file:filename_all().
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The type ascii_string() in the base64 module has been corrected.
The type file:file_info() has been cleaned up.
The type file:fd() has been made opaque in the documentation.
The type nodes() has been removed from erl_bif_types.erl.
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This operation allows pre-allocation of space for files.
It succeeds only on systems that support such operation.
The POSIX standard defines the optional system call
posix_fallocate() to implement this feature. However,
some systems implement more specific functions to
accomplish the same operation.
On Linux, if the more specific function fallocate() is
implemented, it is used instead of posix_fallocate(),
falling back to posix_fallocate() if the fallocate()
call failed (it's only supported for the ext4, ocfs2,
xfs and btrfs file systems at the moment).
On Mac OS X it uses the specific fcntl() operation
F_PREALLOCATE, falling back to posix_fallocate() if
it's available (at the moment Mac OS X doesn't provide
posix_fallocate()).
On any other UNIX system, it uses posix_fallocate() if it's
available. Any other system not providing this system call
or any function to pre-allocate space for files, this operation
always fails with the ENOTSUP POSIX error.
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Expect modifications, additions and corrections.
There is a kludge in file_io_server and
erl_scan:continuation_location() that's not so pleasing.
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* egil/file-info-opt-utc/OTP-7687: (39 commits)
Remove time_t specific test in prim_file_SUITE
Update prim_file.beam and prim_zip.beam
Add types for posixtime_to_universaltime and the reverse
Set BASEYEAR to 1902
Set lower limit of years handled to 1601
Emulate localtime, gmtime and mktime to enable negative time_t
Document file:*_file_info/2
Fix compiler warning in unix_efile.c
Change name of bif universaltime_to_seconds/1
Change options to prim_file:*_file_info/*
Remove dead code
Catch errors from prim_file:*_file_info
Testcase for utc <-> seconds conversion
Fix negative time in seconds_to_universaltime/1
Remove OS taint from datetime conversion
Add utc <-> seconds conversions bifs
Let prim_file validate ctime in file_info
Teach #file_info spec unix epochs for file times
Add file_info_opt tests in prim_file_SUITE
unix_efile: Zero is a valid number in utime
...
Conflicts:
erts/emulator/beam/erl_time_sup.c
erts/emulator/sys/win32/erl_win_sys.h
erts/emulator/sys/win32/sys_time.c
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* file:read_file_info/2
* file:write_file_info/3
Document options and time behavior.
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Since the API for headers/trailers seem to be very awkward to
work with when using non-blocking io the feature is dropped
for now. See unix_efile.c for more details.
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Allow Erlang code to use sendfile() where available by wrapping it as
file:sendfile/4 and file:sendfile/2.
sendfile(2) - Linux man page:
"sendfile() copies data between one file descriptor and another.
Because this copying is done within the kernel, sendfile() is more
efficient than the combination of read(2) and write(2), which would
require transferring data to and from user space."
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An incorrect spec, rpc:yield/1, has been fixed.
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Although the {encoding, encoding()} set of options is documented in
the manual page of the 'file' module, they do not appear in the Mode
description on that page nor in the mode() type declaration.
The patch adds this information in both the code of the module and
the documentation of the module.
To avoid duplication, the declaration of the encoding() type is added
to the 'unicode' module where it most probably belongs.
While at it, added a proper declaration for posix(), took out the
now superfluous information about the types of file:open/2 from the
erl_bif_types module, and corrected the return type of file:open/2
so that it corresponds to the published documentation.
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Signed-off-by: Tuncer Ayaz <[email protected]>
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Add an option that atomically tests for the existence of a file and
creates it if the file does not exist, by passing the O_EXCL flag
to open() on Unix and CREATE_NEW flag on Windows. Support for O_EXCL
varies across platforms and filesystems.
{ok, Fd} = file:open("/tmp/foo", [write,exclusive]),
{error, eexist} = file:open("/tmp/foo", [write,exclusive]).
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Useful for informing the Operating System about the access pattern
for a file's data, so that it can adapt the caching strategy to
maximize disk IO performance.
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file:datasync/1 invokes the POSIX system call "int fdatasync(int fd)".
This system call is similar to "fsync" but, unlike fsync, it does not
update the metadata associated with the file (like the access time for
example). It's used by many DBMSs (MySQL and SQLite of example) to
increase disk IO performance, as it avoids disk seeks and disk write
operations compared to fsync.
More details on it at:
http://linux.die.net/man/2/fdatasync
An example, from the MySQL source:
http://bazaar.launchpad.net/~mysql/mysql-server/mysql-5.1-telco-6.1/annotate/head%3A/mysys/my_sync.c#L61
This new function just calls fsync on systems not implementing fdatasync.
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