Re: Detecting RWF_NOWAIT support
On 12/18/2017 05:28 AM, Goldwyn Rodrigues wrote: On 12/16/2017 08:49 AM, Avi Kivity wrote: On 12/14/2017 09:15 PM, Goldwyn Rodrigues wrote: On 12/14/2017 11:38 AM, Avi Kivity wrote: I'm looking to add support for RWF_NOWAIT within a linux-aio iocb. Naturally, I need to detect at runtime whether the kernel support RWF_NOWAIT or not. The only method I could find was to issue an I/O with RWF_NOWAIT set, and look for errors. This is somewhat less than perfect: - from the error, I can't tell whether RWF_NOWAIT was the problem, or something else. If I enable a number of new features, I have to run through all combinations to figure out which ones are supported and which are not. Here is the return codes for RWF_NOWAIT EINVAL - not supported (older kernel) EOPNOTSUPP - not supported EAGAIN - supported but could not complete because I/O will be delayed Which of these are returned from io_submit() and which are returned in the iocb? These are returned in iocb. Thanks. 0 - supported and I/O completed (success). - RWF_NOWAIT support is per-filesystem, so I can't just remember not to enable RWF_NOWAIT globally, I have to track it per file. Yes, the support is per filesystem. So, the application must know if the filesystem supports it, possibly by performing a small I/O. So the application must know about filesystem mount points, and be prepared to create a file and try to write it (in case the filesystem is empty) or alter its behavior during runtime depending on the errors it sees. Well yes. Hopefully, the application knows what it is doing when it performs RWF_NOWAIT. This type of interface makes it very hard to consume new kernel facilities in a backward compatible way. The kernel should advertise what support it provides; for example this support could be advertised via statx(2). For examples of facilities that advertise their capabilities, see membarrier(2) and KVM.
Re: Detecting RWF_NOWAIT support
On 12/18/2017 05:28 AM, Goldwyn Rodrigues wrote: On 12/16/2017 08:49 AM, Avi Kivity wrote: On 12/14/2017 09:15 PM, Goldwyn Rodrigues wrote: On 12/14/2017 11:38 AM, Avi Kivity wrote: I'm looking to add support for RWF_NOWAIT within a linux-aio iocb. Naturally, I need to detect at runtime whether the kernel support RWF_NOWAIT or not. The only method I could find was to issue an I/O with RWF_NOWAIT set, and look for errors. This is somewhat less than perfect: - from the error, I can't tell whether RWF_NOWAIT was the problem, or something else. If I enable a number of new features, I have to run through all combinations to figure out which ones are supported and which are not. Here is the return codes for RWF_NOWAIT EINVAL - not supported (older kernel) EOPNOTSUPP - not supported EAGAIN - supported but could not complete because I/O will be delayed Which of these are returned from io_submit() and which are returned in the iocb? These are returned in iocb. Thanks. 0 - supported and I/O completed (success). - RWF_NOWAIT support is per-filesystem, so I can't just remember not to enable RWF_NOWAIT globally, I have to track it per file. Yes, the support is per filesystem. So, the application must know if the filesystem supports it, possibly by performing a small I/O. So the application must know about filesystem mount points, and be prepared to create a file and try to write it (in case the filesystem is empty) or alter its behavior during runtime depending on the errors it sees. Well yes. Hopefully, the application knows what it is doing when it performs RWF_NOWAIT. This type of interface makes it very hard to consume new kernel facilities in a backward compatible way. The kernel should advertise what support it provides; for example this support could be advertised via statx(2). For examples of facilities that advertise their capabilities, see membarrier(2) and KVM.
Re: Detecting RWF_NOWAIT support
On 12/16/2017 08:49 AM, Avi Kivity wrote: > > > On 12/14/2017 09:15 PM, Goldwyn Rodrigues wrote: >> >> On 12/14/2017 11:38 AM, Avi Kivity wrote: >>> I'm looking to add support for RWF_NOWAIT within a linux-aio iocb. >>> Naturally, I need to detect at runtime whether the kernel support >>> RWF_NOWAIT or not. >>> >>> >>> The only method I could find was to issue an I/O with RWF_NOWAIT set, >>> and look for errors. This is somewhat less than perfect: >>> >>> - from the error, I can't tell whether RWF_NOWAIT was the problem, or >>> something else. If I enable a number of new features, I have to run >>> through all combinations to figure out which ones are supported and >>> which are not. >> Here is the return codes for RWF_NOWAIT >> EINVAL - not supported (older kernel) >> EOPNOTSUPP - not supported >> EAGAIN - supported but could not complete because I/O will be delayed > > Which of these are returned from io_submit() and which are returned in > the iocb? These are returned in iocb. > >> 0 - supported and I/O completed (success). >> >>> - RWF_NOWAIT support is per-filesystem, so I can't just remember >>> not to >>> enable RWF_NOWAIT globally, I have to track it per file. >> Yes, the support is per filesystem. So, the application must know if the >> filesystem supports it, possibly by performing a small I/O. > > So the application must know about filesystem mount points, and be > prepared to create a file and try to write it (in case the filesystem is > empty) or alter its behavior during runtime depending on the errors it > sees. Well yes. Hopefully, the application knows what it is doing when it performs RWF_NOWAIT. -- Goldwyn
Re: Detecting RWF_NOWAIT support
On 12/16/2017 08:49 AM, Avi Kivity wrote: > > > On 12/14/2017 09:15 PM, Goldwyn Rodrigues wrote: >> >> On 12/14/2017 11:38 AM, Avi Kivity wrote: >>> I'm looking to add support for RWF_NOWAIT within a linux-aio iocb. >>> Naturally, I need to detect at runtime whether the kernel support >>> RWF_NOWAIT or not. >>> >>> >>> The only method I could find was to issue an I/O with RWF_NOWAIT set, >>> and look for errors. This is somewhat less than perfect: >>> >>> - from the error, I can't tell whether RWF_NOWAIT was the problem, or >>> something else. If I enable a number of new features, I have to run >>> through all combinations to figure out which ones are supported and >>> which are not. >> Here is the return codes for RWF_NOWAIT >> EINVAL - not supported (older kernel) >> EOPNOTSUPP - not supported >> EAGAIN - supported but could not complete because I/O will be delayed > > Which of these are returned from io_submit() and which are returned in > the iocb? These are returned in iocb. > >> 0 - supported and I/O completed (success). >> >>> - RWF_NOWAIT support is per-filesystem, so I can't just remember >>> not to >>> enable RWF_NOWAIT globally, I have to track it per file. >> Yes, the support is per filesystem. So, the application must know if the >> filesystem supports it, possibly by performing a small I/O. > > So the application must know about filesystem mount points, and be > prepared to create a file and try to write it (in case the filesystem is > empty) or alter its behavior during runtime depending on the errors it > sees. Well yes. Hopefully, the application knows what it is doing when it performs RWF_NOWAIT. -- Goldwyn
Re: Detecting RWF_NOWAIT support
On 12/16/2017 08:12 PM, vcap...@pengaru.com wrote:
On Sat, Dec 16, 2017 at 10:03:38AM -0800, vcap...@pengaru.com wrote:
On Sat, Dec 16, 2017 at 04:49:08PM +0200, Avi Kivity wrote:
On 12/14/2017 09:15 PM, Goldwyn Rodrigues wrote:
On 12/14/2017 11:38 AM, Avi Kivity wrote:
I'm looking to add support for RWF_NOWAIT within a linux-aio iocb.
Naturally, I need to detect at runtime whether the kernel support
RWF_NOWAIT or not.
The only method I could find was to issue an I/O with RWF_NOWAIT set,
and look for errors. This is somewhat less than perfect:
- from the error, I can't tell whether RWF_NOWAIT was the problem, or
something else. If I enable a number of new features, I have to run
through all combinations to figure out which ones are supported and
which are not.
Here is the return codes for RWF_NOWAIT
EINVAL - not supported (older kernel)
EOPNOTSUPP - not supported
EAGAIN - supported but could not complete because I/O will be delayed
Which of these are returned from io_submit() and which are returned in the
iocb?
0 - supported and I/O completed (success).
- RWF_NOWAIT support is per-filesystem, so I can't just remember not to
enable RWF_NOWAIT globally, I have to track it per file.
Yes, the support is per filesystem. So, the application must know if the
filesystem supports it, possibly by performing a small I/O.
So the application must know about filesystem mount points, and be prepared
to create a file and try to write it (in case the filesystem is empty) or
alter its behavior during runtime depending on the errors it sees.
Can't the application simply add a "nowait" flag to its open file
descriptor encapsulation struct, then in the constructor perform a
zero-length RWF_NOWAIT write immediately after opening the fd to set the
flag? Then all writes branch according to the flag.
According to write(2):
If count is zero and fd refers to a regular file, then write()
may return a failure status if one of the errors below is
detected. If no errors are detected, or error detection is not
performed, 0 will be returned without causing any other effect.
If count is zero and fd refers to a file other than a regular
file, the results are not specified.
So the zero-length RWF_NOWAIT write should return zero, unless it's not
supported.
Oh, I assumed this new flag applied to pwritev2() flags. Disregard my
comment, I see the ambiguity causing your question Avi and do not know
the best approach.
Actually it's not a bad idea. I'm using AIO, not p{read,write}v2, but I
can assume that the response will be the same and that a zero-length
read will return immediately.
Re: Detecting RWF_NOWAIT support
On 12/16/2017 08:12 PM, vcap...@pengaru.com wrote:
On Sat, Dec 16, 2017 at 10:03:38AM -0800, vcap...@pengaru.com wrote:
On Sat, Dec 16, 2017 at 04:49:08PM +0200, Avi Kivity wrote:
On 12/14/2017 09:15 PM, Goldwyn Rodrigues wrote:
On 12/14/2017 11:38 AM, Avi Kivity wrote:
I'm looking to add support for RWF_NOWAIT within a linux-aio iocb.
Naturally, I need to detect at runtime whether the kernel support
RWF_NOWAIT or not.
The only method I could find was to issue an I/O with RWF_NOWAIT set,
and look for errors. This is somewhat less than perfect:
- from the error, I can't tell whether RWF_NOWAIT was the problem, or
something else. If I enable a number of new features, I have to run
through all combinations to figure out which ones are supported and
which are not.
Here is the return codes for RWF_NOWAIT
EINVAL - not supported (older kernel)
EOPNOTSUPP - not supported
EAGAIN - supported but could not complete because I/O will be delayed
Which of these are returned from io_submit() and which are returned in the
iocb?
0 - supported and I/O completed (success).
- RWF_NOWAIT support is per-filesystem, so I can't just remember not to
enable RWF_NOWAIT globally, I have to track it per file.
Yes, the support is per filesystem. So, the application must know if the
filesystem supports it, possibly by performing a small I/O.
So the application must know about filesystem mount points, and be prepared
to create a file and try to write it (in case the filesystem is empty) or
alter its behavior during runtime depending on the errors it sees.
Can't the application simply add a "nowait" flag to its open file
descriptor encapsulation struct, then in the constructor perform a
zero-length RWF_NOWAIT write immediately after opening the fd to set the
flag? Then all writes branch according to the flag.
According to write(2):
If count is zero and fd refers to a regular file, then write()
may return a failure status if one of the errors below is
detected. If no errors are detected, or error detection is not
performed, 0 will be returned without causing any other effect.
If count is zero and fd refers to a file other than a regular
file, the results are not specified.
So the zero-length RWF_NOWAIT write should return zero, unless it's not
supported.
Oh, I assumed this new flag applied to pwritev2() flags. Disregard my
comment, I see the ambiguity causing your question Avi and do not know
the best approach.
Actually it's not a bad idea. I'm using AIO, not p{read,write}v2, but I
can assume that the response will be the same and that a zero-length
read will return immediately.
Re: Detecting RWF_NOWAIT support
On Sat, Dec 16, 2017 at 10:03:38AM -0800, vcap...@pengaru.com wrote: > On Sat, Dec 16, 2017 at 04:49:08PM +0200, Avi Kivity wrote: > > > > > > On 12/14/2017 09:15 PM, Goldwyn Rodrigues wrote: > > > > > > On 12/14/2017 11:38 AM, Avi Kivity wrote: > > > > I'm looking to add support for RWF_NOWAIT within a linux-aio iocb. > > > > Naturally, I need to detect at runtime whether the kernel support > > > > RWF_NOWAIT or not. > > > > > > > > > > > > The only method I could find was to issue an I/O with RWF_NOWAIT set, > > > > and look for errors. This is somewhat less than perfect: > > > > > > > > - from the error, I can't tell whether RWF_NOWAIT was the problem, or > > > > something else. If I enable a number of new features, I have to run > > > > through all combinations to figure out which ones are supported and > > > > which are not. > > > Here is the return codes for RWF_NOWAIT > > > EINVAL - not supported (older kernel) > > > EOPNOTSUPP - not supported > > > EAGAIN - supported but could not complete because I/O will be delayed > > > > Which of these are returned from io_submit() and which are returned in the > > iocb? > > > > > 0 - supported and I/O completed (success). > > > > > > > - RWF_NOWAIT support is per-filesystem, so I can't just remember not > > > > to > > > > enable RWF_NOWAIT globally, I have to track it per file. > > > Yes, the support is per filesystem. So, the application must know if the > > > filesystem supports it, possibly by performing a small I/O. > > > > So the application must know about filesystem mount points, and be prepared > > to create a file and try to write it (in case the filesystem is empty) or > > alter its behavior during runtime depending on the errors it sees. > > Can't the application simply add a "nowait" flag to its open file > descriptor encapsulation struct, then in the constructor perform a > zero-length RWF_NOWAIT write immediately after opening the fd to set the > flag? Then all writes branch according to the flag. > > According to write(2): > >If count is zero and fd refers to a regular file, then write() >may return a failure status if one of the errors below is >detected. If no errors are detected, or error detection is not >performed, 0 will be returned without causing any other effect. >If count is zero and fd refers to a file other than a regular >file, the results are not specified. > > So the zero-length RWF_NOWAIT write should return zero, unless it's not > supported. > Oh, I assumed this new flag applied to pwritev2() flags. Disregard my comment, I see the ambiguity causing your question Avi and do not know the best approach. Cheers, Vito Caputo
Re: Detecting RWF_NOWAIT support
On Sat, Dec 16, 2017 at 10:03:38AM -0800, vcap...@pengaru.com wrote: > On Sat, Dec 16, 2017 at 04:49:08PM +0200, Avi Kivity wrote: > > > > > > On 12/14/2017 09:15 PM, Goldwyn Rodrigues wrote: > > > > > > On 12/14/2017 11:38 AM, Avi Kivity wrote: > > > > I'm looking to add support for RWF_NOWAIT within a linux-aio iocb. > > > > Naturally, I need to detect at runtime whether the kernel support > > > > RWF_NOWAIT or not. > > > > > > > > > > > > The only method I could find was to issue an I/O with RWF_NOWAIT set, > > > > and look for errors. This is somewhat less than perfect: > > > > > > > > - from the error, I can't tell whether RWF_NOWAIT was the problem, or > > > > something else. If I enable a number of new features, I have to run > > > > through all combinations to figure out which ones are supported and > > > > which are not. > > > Here is the return codes for RWF_NOWAIT > > > EINVAL - not supported (older kernel) > > > EOPNOTSUPP - not supported > > > EAGAIN - supported but could not complete because I/O will be delayed > > > > Which of these are returned from io_submit() and which are returned in the > > iocb? > > > > > 0 - supported and I/O completed (success). > > > > > > > - RWF_NOWAIT support is per-filesystem, so I can't just remember not > > > > to > > > > enable RWF_NOWAIT globally, I have to track it per file. > > > Yes, the support is per filesystem. So, the application must know if the > > > filesystem supports it, possibly by performing a small I/O. > > > > So the application must know about filesystem mount points, and be prepared > > to create a file and try to write it (in case the filesystem is empty) or > > alter its behavior during runtime depending on the errors it sees. > > Can't the application simply add a "nowait" flag to its open file > descriptor encapsulation struct, then in the constructor perform a > zero-length RWF_NOWAIT write immediately after opening the fd to set the > flag? Then all writes branch according to the flag. > > According to write(2): > >If count is zero and fd refers to a regular file, then write() >may return a failure status if one of the errors below is >detected. If no errors are detected, or error detection is not >performed, 0 will be returned without causing any other effect. >If count is zero and fd refers to a file other than a regular >file, the results are not specified. > > So the zero-length RWF_NOWAIT write should return zero, unless it's not > supported. > Oh, I assumed this new flag applied to pwritev2() flags. Disregard my comment, I see the ambiguity causing your question Avi and do not know the best approach. Cheers, Vito Caputo
Re: Detecting RWF_NOWAIT support
On Sat, Dec 16, 2017 at 04:49:08PM +0200, Avi Kivity wrote: > > > On 12/14/2017 09:15 PM, Goldwyn Rodrigues wrote: > > > > On 12/14/2017 11:38 AM, Avi Kivity wrote: > > > I'm looking to add support for RWF_NOWAIT within a linux-aio iocb. > > > Naturally, I need to detect at runtime whether the kernel support > > > RWF_NOWAIT or not. > > > > > > > > > The only method I could find was to issue an I/O with RWF_NOWAIT set, > > > and look for errors. This is somewhat less than perfect: > > > > > > - from the error, I can't tell whether RWF_NOWAIT was the problem, or > > > something else. If I enable a number of new features, I have to run > > > through all combinations to figure out which ones are supported and > > > which are not. > > Here is the return codes for RWF_NOWAIT > > EINVAL - not supported (older kernel) > > EOPNOTSUPP - not supported > > EAGAIN - supported but could not complete because I/O will be delayed > > Which of these are returned from io_submit() and which are returned in the > iocb? > > > 0 - supported and I/O completed (success). > > > > > - RWF_NOWAIT support is per-filesystem, so I can't just remember not to > > > enable RWF_NOWAIT globally, I have to track it per file. > > Yes, the support is per filesystem. So, the application must know if the > > filesystem supports it, possibly by performing a small I/O. > > So the application must know about filesystem mount points, and be prepared > to create a file and try to write it (in case the filesystem is empty) or > alter its behavior during runtime depending on the errors it sees. Can't the application simply add a "nowait" flag to its open file descriptor encapsulation struct, then in the constructor perform a zero-length RWF_NOWAIT write immediately after opening the fd to set the flag? Then all writes branch according to the flag. According to write(2): If count is zero and fd refers to a regular file, then write() may return a failure status if one of the errors below is detected. If no errors are detected, or error detection is not performed, 0 will be returned without causing any other effect. If count is zero and fd refers to a file other than a regular file, the results are not specified. So the zero-length RWF_NOWAIT write should return zero, unless it's not supported. Regards, Vito Caputo
Re: Detecting RWF_NOWAIT support
On Sat, Dec 16, 2017 at 04:49:08PM +0200, Avi Kivity wrote: > > > On 12/14/2017 09:15 PM, Goldwyn Rodrigues wrote: > > > > On 12/14/2017 11:38 AM, Avi Kivity wrote: > > > I'm looking to add support for RWF_NOWAIT within a linux-aio iocb. > > > Naturally, I need to detect at runtime whether the kernel support > > > RWF_NOWAIT or not. > > > > > > > > > The only method I could find was to issue an I/O with RWF_NOWAIT set, > > > and look for errors. This is somewhat less than perfect: > > > > > > - from the error, I can't tell whether RWF_NOWAIT was the problem, or > > > something else. If I enable a number of new features, I have to run > > > through all combinations to figure out which ones are supported and > > > which are not. > > Here is the return codes for RWF_NOWAIT > > EINVAL - not supported (older kernel) > > EOPNOTSUPP - not supported > > EAGAIN - supported but could not complete because I/O will be delayed > > Which of these are returned from io_submit() and which are returned in the > iocb? > > > 0 - supported and I/O completed (success). > > > > > - RWF_NOWAIT support is per-filesystem, so I can't just remember not to > > > enable RWF_NOWAIT globally, I have to track it per file. > > Yes, the support is per filesystem. So, the application must know if the > > filesystem supports it, possibly by performing a small I/O. > > So the application must know about filesystem mount points, and be prepared > to create a file and try to write it (in case the filesystem is empty) or > alter its behavior during runtime depending on the errors it sees. Can't the application simply add a "nowait" flag to its open file descriptor encapsulation struct, then in the constructor perform a zero-length RWF_NOWAIT write immediately after opening the fd to set the flag? Then all writes branch according to the flag. According to write(2): If count is zero and fd refers to a regular file, then write() may return a failure status if one of the errors below is detected. If no errors are detected, or error detection is not performed, 0 will be returned without causing any other effect. If count is zero and fd refers to a file other than a regular file, the results are not specified. So the zero-length RWF_NOWAIT write should return zero, unless it's not supported. Regards, Vito Caputo
Re: Detecting RWF_NOWAIT support
On 12/14/2017 09:15 PM, Goldwyn Rodrigues wrote: On 12/14/2017 11:38 AM, Avi Kivity wrote: I'm looking to add support for RWF_NOWAIT within a linux-aio iocb. Naturally, I need to detect at runtime whether the kernel support RWF_NOWAIT or not. The only method I could find was to issue an I/O with RWF_NOWAIT set, and look for errors. This is somewhat less than perfect: - from the error, I can't tell whether RWF_NOWAIT was the problem, or something else. If I enable a number of new features, I have to run through all combinations to figure out which ones are supported and which are not. Here is the return codes for RWF_NOWAIT EINVAL - not supported (older kernel) EOPNOTSUPP - not supported EAGAIN - supported but could not complete because I/O will be delayed Which of these are returned from io_submit() and which are returned in the iocb? 0 - supported and I/O completed (success). - RWF_NOWAIT support is per-filesystem, so I can't just remember not to enable RWF_NOWAIT globally, I have to track it per file. Yes, the support is per filesystem. So, the application must know if the filesystem supports it, possibly by performing a small I/O. So the application must know about filesystem mount points, and be prepared to create a file and try to write it (in case the filesystem is empty) or alter its behavior during runtime depending on the errors it sees.
Re: Detecting RWF_NOWAIT support
On 12/14/2017 09:15 PM, Goldwyn Rodrigues wrote: On 12/14/2017 11:38 AM, Avi Kivity wrote: I'm looking to add support for RWF_NOWAIT within a linux-aio iocb. Naturally, I need to detect at runtime whether the kernel support RWF_NOWAIT or not. The only method I could find was to issue an I/O with RWF_NOWAIT set, and look for errors. This is somewhat less than perfect: - from the error, I can't tell whether RWF_NOWAIT was the problem, or something else. If I enable a number of new features, I have to run through all combinations to figure out which ones are supported and which are not. Here is the return codes for RWF_NOWAIT EINVAL - not supported (older kernel) EOPNOTSUPP - not supported EAGAIN - supported but could not complete because I/O will be delayed Which of these are returned from io_submit() and which are returned in the iocb? 0 - supported and I/O completed (success). - RWF_NOWAIT support is per-filesystem, so I can't just remember not to enable RWF_NOWAIT globally, I have to track it per file. Yes, the support is per filesystem. So, the application must know if the filesystem supports it, possibly by performing a small I/O. So the application must know about filesystem mount points, and be prepared to create a file and try to write it (in case the filesystem is empty) or alter its behavior during runtime depending on the errors it sees.
Re: Detecting RWF_NOWAIT support
On 12/14/2017 11:38 AM, Avi Kivity wrote: > I'm looking to add support for RWF_NOWAIT within a linux-aio iocb. > Naturally, I need to detect at runtime whether the kernel support > RWF_NOWAIT or not. > > > The only method I could find was to issue an I/O with RWF_NOWAIT set, > and look for errors. This is somewhat less than perfect: > > - from the error, I can't tell whether RWF_NOWAIT was the problem, or > something else. If I enable a number of new features, I have to run > through all combinations to figure out which ones are supported and > which are not. Here is the return codes for RWF_NOWAIT EINVAL - not supported (older kernel) EOPNOTSUPP - not supported EAGAIN - supported but could not complete because I/O will be delayed 0 - supported and I/O completed (success). > > - RWF_NOWAIT support is per-filesystem, so I can't just remember not to > enable RWF_NOWAIT globally, I have to track it per file. Yes, the support is per filesystem. So, the application must know if the filesystem supports it, possibly by performing a small I/O. -- Goldwyn
Re: Detecting RWF_NOWAIT support
On 12/14/2017 11:38 AM, Avi Kivity wrote: > I'm looking to add support for RWF_NOWAIT within a linux-aio iocb. > Naturally, I need to detect at runtime whether the kernel support > RWF_NOWAIT or not. > > > The only method I could find was to issue an I/O with RWF_NOWAIT set, > and look for errors. This is somewhat less than perfect: > > - from the error, I can't tell whether RWF_NOWAIT was the problem, or > something else. If I enable a number of new features, I have to run > through all combinations to figure out which ones are supported and > which are not. Here is the return codes for RWF_NOWAIT EINVAL - not supported (older kernel) EOPNOTSUPP - not supported EAGAIN - supported but could not complete because I/O will be delayed 0 - supported and I/O completed (success). > > - RWF_NOWAIT support is per-filesystem, so I can't just remember not to > enable RWF_NOWAIT globally, I have to track it per file. Yes, the support is per filesystem. So, the application must know if the filesystem supports it, possibly by performing a small I/O. -- Goldwyn
Detecting RWF_NOWAIT support
I'm looking to add support for RWF_NOWAIT within a linux-aio iocb. Naturally, I need to detect at runtime whether the kernel support RWF_NOWAIT or not. The only method I could find was to issue an I/O with RWF_NOWAIT set, and look for errors. This is somewhat less than perfect: - from the error, I can't tell whether RWF_NOWAIT was the problem, or something else. If I enable a number of new features, I have to run through all combinations to figure out which ones are supported and which are not. - RWF_NOWAIT support is per-filesystem, so I can't just remember not to enable RWF_NOWAIT globally, I have to track it per file. Did I miss another method of detecting RWF_NOWAIT?
Detecting RWF_NOWAIT support
I'm looking to add support for RWF_NOWAIT within a linux-aio iocb. Naturally, I need to detect at runtime whether the kernel support RWF_NOWAIT or not. The only method I could find was to issue an I/O with RWF_NOWAIT set, and look for errors. This is somewhat less than perfect: - from the error, I can't tell whether RWF_NOWAIT was the problem, or something else. If I enable a number of new features, I have to run through all combinations to figure out which ones are supported and which are not. - RWF_NOWAIT support is per-filesystem, so I can't just remember not to enable RWF_NOWAIT globally, I have to track it per file. Did I miss another method of detecting RWF_NOWAIT?
