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Re: [libvirt] [PATCH 1/5] Add virFileLock and virFileUnlock APIs



On Wed, Aug 10, 2011 at 16:37:24 +0100, Daniel P. Berrange wrote:
> From: "Daniel P. Berrange" <berrange redhat com>
> 
> Add some simple wrappers around the fcntl() discretionary file
> locking capability.
> 
> * src/util/util.c, src/util/util.h, src/libvirt_private.syms: Add
>   virFileLock and virFileUnlock APIs
> ---
>  src/libvirt_private.syms |    2 +
>  src/util/virfile.c       |   83 ++++++++++++++++++++++++++++++++++++++++++++++
>  src/util/virfile.h       |    3 ++
>  3 files changed, 88 insertions(+), 0 deletions(-)
> 
> diff --git a/src/libvirt_private.syms b/src/libvirt_private.syms
> index 830222b..261f3e0 100644
> --- a/src/libvirt_private.syms
> +++ b/src/libvirt_private.syms
> @@ -1039,6 +1039,7 @@ virFileFindMountPoint;
>  virFileHasSuffix;
>  virFileIsExecutable;
>  virFileLinkPointsTo;
> +virFileLock;
>  virFileMakePath;
>  virFileMatchesNameSuffix;
>  virFileOpenAs;
> @@ -1051,6 +1052,7 @@ virFileReadPidPath;
>  virFileResolveLink;
>  virFileSanitizePath;
>  virFileStripSuffix;
> +virFileUnlock;
>  virFileWaitForDevices;
>  virFileWriteStr;
>  virFindFileInPath;
> diff --git a/src/util/virfile.c b/src/util/virfile.c
> index 8b32518..1346c1a 100644
> --- a/src/util/virfile.c
> +++ b/src/util/virfile.c
> @@ -251,3 +251,86 @@ virFileDirectFdFree(virFileDirectFdPtr dfd)
>      virCommandFree(dfd->cmd);
>      VIR_FREE(dfd);
>  }
> +
> +
> +#ifndef WIN32
> +/**
> + * virFileLock:
> + * @fd: file descriptor to acquire the lock on
> + * @shared: type of lock to acquire
> + * @start: byte offset to start lock
> + * @len: length of lock (0 to acquire entire remaining file from @start)
> + *
> + * Attempt to acquire a lock on the file @fd. If @shared
> + * is true, then the a shared lock will be acquired,
s/the //            ^^^^^

> + * otherwise an exclusive lock will be acquired. If
> + * the lock cannot be acquired, an error will be
> + * returned. This will not wait to acquire the lock if
> + * another process already holds it.
> + *
> + * The lock will be released will @fd is closed. The lock
s/will/when/ I guess            ^^^^

> + * will also be released if *any* other open file descriptor
> + * pointing to the same underlying file is closed. As such
> + * this function should not be relied on in multi-threaded
> + * apps where other threads can be opening/closing arbitrary
> + * files.
> + *
> + * Returns: 0 on success, or -errno otherwise
The documentation builder doesn't want ':' after "Returns" IIRC. Ah, but this
is not a public API and documentation won't be generated from this block
anyway so it doesn't really matter.

> + */
> +int virFileLock(int fd, bool shared, off_t start, off_t len)
> +{
> +    struct flock fl = {
> +        .l_type = shared ? F_RDLCK : F_WRLCK,
> +        .l_whence = SEEK_SET,
> +        .l_start = start,
> +        .l_len = len,
> +    };
> +
> +    if (fcntl(fd, F_SETLK, &fl) < 0)
> +        return -errno;
> +
> +    return 0;
> +}
> +
> +
> +/**
> + * virFileUnlock:
> + * @fd: file descriptor to release the lock on
> + * @start: byte offset to start unlock
> + * @len: length of lock (0 to release entire remaining file from @start)
> + *
> + * Release a lock previously acquired with virFileUnlock().
> + * NB the lock will also be released if any open file descriptor
> + * pointing to the same file as @fd is closed
> + *
> + * Returns 0 on succcess, or -errno on error
> + */
> +int virFileUnlock(int fd, off_t start, off_t len)
> +{
> +    struct flock fl = {
> +        .l_type = F_UNLCK,
> +        .l_whence = SEEK_SET,
> +        .l_start = start,
> +        .l_len = len,
> +    };
> +
> +    if (fcntl(fd, F_SETLK, &fl) < 0)
> +        return -errno;
> +
> +    return 0;
> +}
> +#else
> +int virFileLock(int fd ATTRIBUTE_UNUSED,
> +                bool shared ATTRIBUTE_UNUSED,
> +                off_t start ATTRIBUTE_UNUSED,
> +                off_t len ATTRIBUTE_UNUSED)
> +{
> +    return -ENOSYS;
> +}
> +int virFileUnlock(int fd ATTRIBUTE_UNUSED,
> +                  off_t start ATTRIBUTE_UNUSED,
> +                  off_t len ATTRIBUTE_UNUSED)
> +{
> +    return -ENOSYS;
> +}
> +#endif
> diff --git a/src/util/virfile.h b/src/util/virfile.h
> index 0906568..e025614 100644
> --- a/src/util/virfile.h
> +++ b/src/util/virfile.h
> @@ -65,4 +65,7 @@ int virFileDirectFdClose(virFileDirectFdPtr dfd);
>  
>  void virFileDirectFdFree(virFileDirectFdPtr dfd);
>  
> +int virFileLock(int fd, bool shared, off_t start, off_t len);
> +int virFileUnlock(int fd, off_t start, off_t len);
> +
>  #endif /* __VIR_FILES_H */

ACK with nits fixed.

Jirka


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